Thursday, March 3, 2011

It might seem contrary to discuss FTL only after a post on interstellar empire, a concept that pretty much depends on star travel being cheap, convenient, and above all fast. (Yes, there are STL scenarios, but they are so stretchy that violating General Relativity suspends less disbelief.)

But in broader perspective it is our desire for interstellar empire, or other such cool settings, that calls out for the willing suspension of disbelief in the first place. All spaceships, as a commenter on this blog once observed, travel at the speed of plot, but that is especially true when it comes to FTL. Spaceships in the Plausible Midfuture have some of the constraints of real-world vehicles, and plots must work around them, but the only constraint on FTL is that it must sound convincing to readers who want to be convinced, at least while reading the story. (Although FTL systems in SF not infrequently fail even at that.)

Unlike last post, this time I remembered to link the relevant page at Atomic Rockets, which covers or links the relevant physics and pseudo-physics, and offers some useful FTL typologies. Also a link to my observation in the Tough Guide to the Known Galaxy that all FTL tech is equivalent to flipping tarot cards while chanting in Welsh - i.e., effectively it is magic.

And a post here from last year which noted that contemporary physics has just barely left the door open to FTL, subject to certain constraints. The relevant effect of these constraints - as I understand it (and General Relativity is not my field of expertise) - is that you can stay out of temporal trouble so long as your baseline FTL routes do not cross-connect.

To follow the rapid transit metaphor I used in that post, you can have multiple routes out from Earth (via wormholes or whatever), with as many branches and sub-branches as you want, and travel times can be as fast as you want them to be. But each station can only be on one line. If you can take two separate routings to reach a given destination, of differing length, then you have to pay the temporal piper.

For example, from Sol to Sirius is 8.6 light years, while from Sol to Wolf 359 is 9.0 light years. Given tramlines equipped with a suitable array of oscillating hands, you can reach either one in in a month by your onboard clock, or an hour, and return in similar time. In Earth's frame of reference, going outbound you are in fact travelling nearly a decade into the future, and returning you are going nearly a decade into the past. This produces no awkward time-travel-esque results, because you don't return to Earth before you left, and you can't get back to Sirius for a second visit prior to your first one.

From Wolf 359 to Sirius is 7.7 light years, so the roundabout route to Sirius via Wolf 359 is 16.7 light years. If you could simply open another tramline, you could travel to Sirius via the indirect route, arrive there 17 years from now, read some stock quotes, return by the same roundabout route to Earth, then go by the direct route, and invest in Sirian stocks years earlier. Big trouble, and not just for stock markets.

So, to avoid breaking causality, such routings must be ruled out, or at least force you to twiddle thumbs those extra eight years instead of raking in a bundle. I don't begin to understand the required coefficient of jive, but apparently it can be done without violating General Relativity, at the price of making such roundabout routings very inconvenient.

(Commenters who do understand this stuff are welcome - indeed, invited - to step in and expand on / correct these points.)

The hitch is that for story purposes we probably want those roundabout routings - not to travel into the past, but merely to run blockades and the like.

My impression is that there is still a workaround. Simply assume that all FTL travel to Sirius proceeds via Wolf 359, but that there are separate 'local' and 'express' tramlines along the route - the former stopping off at Wolf 359, while the latter passes right through without entering normal space.

If each entry or exit from a tramline involves a cost (e.g., reaching the jump point through normal space), then regular Sol-Sirius travel would follow the express tramline, passing by Wolf 359 nonstop. But the local routing, stopping off in normal space at Wolf 359, would remain available when needed for story purposes.

Yes, this is more than a little strained (and possibly downright wrong), but hey, we're talking about FTL. The alternative, so far as I can see, is simply blowing off a lot of well-establish physics entirely. Remember, it isn't as if Einstein kicked Newton onto the ash heap; old Sir Isaac still gives an approximation good enough for interplanetary travel planning.

Moreover, the above gimmickry can be almost entirely buried out of sight, at least so long as your intended flavor of FTL is jump-oriented, and you don't get deeply into the weeds about the sequence in which routes were established in the first place.

Having said that, this approach should probably be left to physicists, or people who do General Relativity as a hobby, and might as well be physicists.

My more general advice on FTL - which I seem to have arrived at via Wolf 359 - is to say as little about the mechanism as possible. Don't talk about wormholes, don't talk about Alcubierre, or any other present-day speculation. All you will do is date yourself, because I don't need to travel into the future to guess that these particular edge-of-the-envelope speculations will be superceded.

Bury all that theoretical stuff under a couple of toss-off jargon terms - Horst-Milne congruencies, Alderson Drive, whatever - and concentrate on what actually matters, which is how FTL actually operates in a setting: size and cost of the gizmo, apparent travel times, available routings, and so forth.

322 comments:

Someone with more time can verify this, but my understanding of semi plausible wormhole physics is that if two wormholes with different frames of reference are brought close to each other, they will create fields of virtual particles that will ultimately destroy the wormholes before the closed timelike curve can be established.

From Wikipedia:

"In 1993, Matt Visser argued that the two mouths of a wormhole with such an induced clock difference could not be brought together without inducing quantum field and gravitational effects that would either make the wormhole collapse or the two mouths repel each other.[32] Because of this, the two mouths could not be brought close enough for causality violation to take place. However, in a 1997 paper, Visser hypothesized that a complex "Roman ring" (named after Tom Roman) configuration of an N number of wormholes arranged in a symmetric polygon could still act as a time machine, although he concludes that this is more likely a flaw in classical quantum gravity theory rather than proof that causality violation is possible"

As I just posted over in the Empires thread, the speed of your FTL is a limit on the effective size of your empire.

If your FTL comms are packet-ships (or jump-point drones), then you are limited to 'controlling' an area of about .5ly around the jump-point. Anything farther than that, the empire can't respond quickly enough.

Note that the .5ly distance is the *total* realspace distance your messages need to travel through, so if you have multiple jumps, you have less control around them.

As I understand things, causality is maintained as long as you don't leave Wolf 359 before you left Earth, and you don't leave Sirius before you left Wolf 359. Given the slight relative proper motions of those three stars, that shouldn't be too tough a criterion to satisfy. The trick is expanding the frame of reference to include all nodes in the circuit, and not doing anything crazy inside that reference frame.

Rick, there's actually one way to get around all of this, and IIRC is actually required for some aspects of wormholes to work:

Special frame of reference.

If all FTL travel necessarily takes on the same reference frame in its operation, there's no violation of causality. It strikes fear into the hearts of GR adherents, yes. It would, however, make a certain sense to laypeople - if your FTL physics involve shortcuts outside the universe, then you'd take on the frame of reference outside the universe. Not exactly how the math works, of course, but close enough.

Note this works much better for Alcubierre drive than wormholes.

For wormholes, imagine that instead of the discontinuity expected, there's a tunnel(-like thing). Normally the causality-violating circumstances of wormholes requires one end to be accelerated to relativistic velocity, then decelerated. If there's an arbitrarily short tunnel of spacetime between the two, then said tunnel can "stretch" if the ends are at relativistic velocity with respect to each other. IANAGRE (I am not a general relativity expert), but given we don't understand quantum gravity, there's plenty of room for handwavium.

IANAGRE either, but AIUI a lot of what goes on with wormholes and time travel is based on a misunderstanding of relativistic time dilation. When one travels at relatvisitic velocities, one is not falling behind in time. One is moving forward in time, but one's clocks (all clocks: chemical, nuclear, quantum; not just the tick-tock kind) are moving slower. When you slow down, you're not arriving in the past of any frame of reference you are connected with. You are arriving in the present. If you turn around and go back to your starting point, you do not arrive in any other time than the present, WRT to that reference frame.

Sending information from a relativistic wormhole mouth to one (relatively) at rest does not send information back in time. It sends the information in a state consistent with the rest frame. For example, if you travel 4 light years at a .5 time dilation factor, then stop and send back observations of the star field at your point, you don't send back information from four years in the future of the other end of the wormhole. You send back information from that end's present. It just doesn't take four years to get there. But if you sent that same message by radio, guess what? Four years from now the recipient would get information that precisely agrees with information you sent through the wormhole.

I have yet to see someone explain the causality problem with wormholes. I've seen the argument numerous times, but it seems like there are some key assumptions missing.

I will note that everything is in motion. Most things are moving dramatically different velocities. So if you open one end of a wormhole on Earth, and another on some planet on Tau Ceti, there will be a huge discrepancy in the conservation of momentum if anything passes through. I suspect a wormhole drive would require syncing up both ends so that they are both stationary relative to one another. Or, a canceling "momentum wave" would have to emminate from both ends, so that the net momentum of the transported mass zeroes out.

A reply I got from the chap who maintains the site below (at least I think it's him, can't find the original email :P ) re a hyperspace model that may work:

http://www.physicsguy.com/ftl/html/FTL_intro.html

"In my own SF universe, I basically have a similar desire for an FLT technology. What I employ is sort of like the idea of hyperspace (or sub-space, if you like). However, my hyperspace-like concept has a special feature: it has a specific frame of reference at every point in our space-time. When you enter hyperspace (to go FTL), you automatically take on the frame of reference of hyperspace.

If you've looked through my web site, then you might have seen me discuss this basic concept. In general, if you can take two FTL trips in two different frames of reference, you can end up where you started before you left (your first trip is FTL in frame 1, but backward in time in frame 2, and your second trip (after you accelerate to frame 2) is FTL in frame 2 but backwards in time in frame 1). In any case, if hyperspace forces you to have a specific frame of reference when you go to travel FTL, then this paradox is solved.

Technically, you are violating relativity by defining a special frame of reference. However, if that special frame applies only to the use of hyperspace and not to other areas of physics, then you can argue that the special frame of reference, while technically violating relativity, does not effect any other areas of physics for your universe. Basically you get to say "Einstein was right... just for realspace."

You could have something like a "light-cone" in the hyperspace frame of reference, but basically there's no need. If hyperspace does not define a special frame of reference, then having another light-speed like concept in hyperspace would not prevent you from violating causality in normal space. If hyperspace does define a special frame of reference, then theoretically you could travel at infinite speed in that frame of reference (connecting any two events that happen simultaneously in the hyperspace frame of reference) and you still wouldn't have any problems with causality.

That's not to say that this conceptual technology might not pose other problems with basic physics (e.g., it's possible that you could violate angular momentum conservation), but these issues are probably a little "down in the weeds" compared to relativity and causality."

The whole point of GR is that there is no rest frame. Under the traditional wormhole geometry, the two ends of the wormhole share a reference frame between them.

When one end is accelerated to relativistic speed, the subjective distance to the destination is compressed. The "rest" frame would see the same apparent spacial compression when looking through the wormhole.

Say a wormhole is created, and one end sent off towards Tau Ceti at sufficient velocity for a dilation factor of 0.1. When observing the far end on its travels from Earth, it would appear to take just over 30 years. For an observer traveling with the far end it would take 3 years. An observer looking through the wormhole on Earth, however, would also see the journey take 3 years.

From the POV of the "rest" frame, no, there's no travel into the past. There is, however, travel into the future. It's from the POV of the far end that there is travel to the past, and that's where causality gets tricky.

Citizen Joe:

See above sorta-explanation.

"So if you open one end of a wormhole on Earth, and another on some planet on Tau Ceti..."

Not how it works (in theory). You have to open both ends together in spacetime, and then move them around. That's where the time loops come in, depending on the arrangement.

The key assumption is that the two ends share a reference frame. I don't know enough about tensors to do the math myself, so I'm not sure if that's an assumption or a result. I suspect the former, since the examinations of wormholes so far have been exact solutions in GR (which usually entail starting with the desired spacetime configuration and working backwards), but I can't be sure.

I always visualized wormholes and warp drives as ways of 'bypassing' distance (I know that that is a simplification of the highest order); if it takes any amount of time whatsoever (or even no time), then there is no real violation of causualty; it's just an illusion.

On another note, how much energy is needed to move X amount of cubic meters of mass through FTL? Is it going to be a brute-force approch, or is it more technique? Will it just be shovel petrawatts into a tiny space, or will it be more like this mix of exotic particles at this power density at this energy level? Or are you just going to say "ok, punch in the target coordinants and flip the switch on the Zoom-o-tron(tm)" and then you are there. The one thing that almost everyone has said is that whatever you do, be consistant. If you have to use stupindously huge amounts of energy for your FTL, then you should have massive amounts of energy available for your sublight drive as well.

The thought occures to me that, depending on the rate or percentage of distance that you are bypassing, you could use it as an STL drive as well. Say you have a process that 'tunnels' through the 'extra diemensions' that some physisis theorize exsit, and you can use it to bypass 99% of distance; you want to travel 300 million kilometers away and your ship can reach 30Kps; you accelerate to 30 KPS and then turn on your drive. So now you only have to 'travel' 3 million kilometers, and at 30 Kps, it should only take you 100,000 seconds, or about 27.78 hours; still STL, but really fast. Now, use another version of the same drive, only this one will bypass 99.9% of distance; now your trip only takes 2.778 hours; use another version that bypasses 99.9999% of distance and now your trip will only last 0.002778 hours. And all with you having a ship that only needs to reach 30 Kps delta-V. Now to figure out how much power it needs and how that power is applied.

I find none of this remotely as plausible as STL interestellar empires. For FTL, you need to dump Einstein. For STL empires, you need to dump your cultural assumptions. And you choose to dump Einstein?

If you're going to have FTL, you're leaving behind objective reality as we know it. So you might as well go whole hog and have FTL be (quasi-)supernatural, like in Frank Herbert's Dune. The superpower that enables FTL in Dune also enables other violations of causality which the story explores in detail... nice symmetry which fits our understanding of space-time and FTL doesn't feel like a deus ex machina anymore.If you're going to undermine our sense of reality, make it interesting! Have FTL solve some tantalizaing question like Fermi's paradox. Maybe FTL-endowed aliens have interacted with humans in the past. Maybe people (and other beings) really do have spirits and FTL travel happens through the spirit world.If you read a Lovecraftian story you're not going to wonder if the Ancients' interstellar gate in Antarctica is violating GR.

Raymond - To be honest, I’m not seeing the causality problem from what I understand of wormholes. Granted, what I know of wormholes wouldn’t come close to filling up the vacuum that is SyFy, but still it’s something to start with.

From what I understand of how Rick describes the wormhole-based FTL highway system, wormholes are able to be generated but one of the mouths (and their associated stabilization “Stargate” equipment) has to be “towed” to their intended destination by an STL spacecraft since there is no other way to use FTL and each mouth is large enough to accommodate a non-Wormhole STL Transport craft at maximum. Now, if I understand correctly, both wormhole mouths share a similar time frame (i.e. The Present) on either end which can be traversed by any individual. Since the wormhole/spacecraft/whatever has not technically left the time frame of, let’s say the Earth for sake of argument and the effects of time dilation is only apparent when one accelerates to a velocity higher than an observer on earth and returns from said velocity, then I’m not really seeing a violation of causality myself. I know the argument is that the wormhole mouth that’s being towed is traveling at time dilating velocities and thus is technically travelling to the future, but if there is still free movement up and down the wormhole tunnel during transit then wouldn’t it mean that it’s still the present on either side of the wormhole?

As for trying to forsee stocks on a wormhole that is “in the future” relative to the one “in the past”, personally I don’t see that kind of time travel since there is a notable checkpoint for all transport and communications since there’s no FTL communication that is independent of the wormhole network. I simply don’t get it.

As for Horselover Fat’s two cents on FTL and Einstein, well there has been some recent development (admittedly on the quantum level) that shows time travel interference with the past is virtually impossible due to some kind of wave interference phenomenon whose technical term I can’t immediately recall but reinforces the Consistency Protection that prevents any possible paradox. Einstein did theorize that FTL is equal to Time Travel, but that doesn’t ultimately mean that any potential time travelers would do anything to mess up said timeline. And even then that’s assuming that there isn’t some kind of fundamental barrier that prevents any FTL spacecraft from moving anywhere along the timeline other than forward lest said craft is vaporized into quarks.

Probably one reason why jump points, wormholes and hyperspace-esque parallel space-times are so popular over trying to accelerate beyond the speed of light nowadays: There’s no violation to General Relativity and Causality if you’re not technically traveling faster than the speed of light.

And Lovecraftien beings a part of FTL travel plane in a Science Fiction setting Horselover? Allow me to direct you to the Immaterium of the Warhammer 40K franchise.

The way I see it, scifi is about speculative futures. We're happy with speculative history, right? We all know what really happened but are willing to entertain "what if?" scenarios. Some alternative history plays very hard with the facts such as "This one turning point really could have gone either way so we'll just make it go the other way and run from there." And some go really far like the question of whether the steam engine could have really been invented in the time of the Greeks and what that would have meant.

Most fans are willing to entertain even wildly improbable scenarios if presented with enough verve and panache.

So that's how I view scifi. Really, really hard scifi is about what you think is most likely to happen. You may be off, you may be really, really off, but it's an honest effort. If you soften it up a little, make some assumptions that might not seem as likely, if it's in the service of telling an interesting story and you stick by your guns, there's a good chance of writing a story worth telling.

And Lovecraftien beings a part of FTL travel plane in a Science Fiction setting Horselover? Allow me to direct you to the Immaterium of the Warhammer 40K franchise.

Space monsters are actually older than that, though I do think 40k will be what most people think of when you bring them up. i think that's taken precedence over Trek's space crystals and space ameobae.

It took me a decade to wrap my head around the causality problems; I know it's confusing as hell. So let's put it slightly differently:

You know the old story where you get in a ship, say in the year 2100, accelerate to relativistic speed, and come back? Where a hundred years have passed on Earth but it only took you a year? Take a wormhole with you.

When the ship gets back to Earth, your watch says 2101 (it only took you a year, right?). The clock on ship-side!earth says 2200. The clock at the stayed-at-home end is in 2101, just like your watch.

I'm familiar with the 40k fluff but when I say I want monsters in my hyperspace setting, people immediately go "Oh, you mean the Warp." People no longer say "Oh, the crystalline entity from the TNG pilot."

Now I know 40k is supposed to be grimdark but I never liked the trope of "plenty of hell dimensions and demons but no heaven dimensions, no angels." Can't find the term to describe that but it gets old to have it all monsters all the time. It really gets grating when the demons are all cast in the Christian context. Wait, that's the only part of the cosmology that's real in this setting? That sucks!

When the ship gets back to Earth, your watch says 2101 (it only took you a year, right?). The clock on ship-side!earth says 2200. The clock at the stayed-at-home end is in 2101, just like your watch.

So if one subjective month passed on the ship and 12 months passed on Earth, then once it brings the wormhole back, I would be able to go through it to reappear 11 months ago? If I went through the day they arrived back home I would emerge on the ship sometime in the past. Once the ship is at rest with Earth and I wait a full year after arrival, going through the wormhole would bring me to a month after it arrived?

"So if one subjective month passed on the ship and 12 months passed on Earth, then once it brings the wormhole back, I would be able to go through it to reappear 11 months ago? If I went through the day they arrived back home I would emerge on the ship sometime in the past. Once the ship is at rest with Earth and I wait a full year after arrival, going through the wormhole would bring me to a month after it arrived?"

Yep.

Assuming, as I've been doing, the traditional wormhole geometry, with the actual wormhole having zero distance (and thus linking the two frames of reference).

"The math bears all this out?"

As far as I can tell, not being able to work with tensor calculus myself.

But what if we leave wormholes out of it? Does FTL still imply time travel?

I know causality is all tied up with the speed of light and the conveying of information but I don't feel it with the same intuitive sense of realities in the physical world like don't drop that glass, don't touch a hot pan, etc.

"But what if we leave wormholes out of it? Does FTL still imply time travel?"

Yes. Unless qualified by a special frame of reference which all FTL is conducted in (as Teleros and I mentioned earlier - the link he gave is quite helpful). You can set up scenarios (with suitable relativistic velocities) where events that appear simultaneous to one observer are separated in time to another. Thus, if information can be transmitted between reference frames faster than light, causality can be violated.

"I know causality is all tied up with the speed of light and the conveying of information but I don't feel it with the same intuitive sense of realities in the physical world like don't drop that glass, don't touch a hot pan, etc."

Ok, I do understand the 'frames of reference', but just because I can see the past, doesn't mean that I can go there; it still seems to me that, while you are discribing the frames of reference of the wormhole mouths, the frames of reference of the Earth and the spaceship remain the same and it is still an illusion; after all, I can see the past with a telescope, but if I were to be instantaniously transported to that local, it would still be in the present. It seems that the information passing through the wormhole is affected by time dialation, but the observers are not; so if I step back through your wormhole, even though I feel that it is 2101, once I get back to Earth, it will still be 2200, even though I still 'feel' like only a month has gone by. Besides, once you've slowed down and have come to rest relative to the Earth end, the space it opens up to will still be in the 'present' relaitive to the Earth. I know that the math is suppose to prove actual time travel, but I still think that it just proves how the illusion works; now, if we only had a wormhole and a relativistic spaceship we could prove it one way or the other; I'd be quite happy to be proven wrong.

Horselover Fat: "I find none of this remotely as plausible as STL interestellar empires. For FTL, you need to dump Einstein. For STL empires, you need to dump your cultural assumptions. And you choose to dump Einstein?"

That's why we only try to dump Einstein a little bit :P . Like with my above post for example.

"Maybe people (and other beings) really do have spirits and FTL travel happens through the spirit world."

PURGE THE HERETIC!

...

Sorry, got carried away. But yeah, if you've got FTL in the spirit world, everyone will just think "oh it's like 40K".

Ferrell: yeah, it's definitely difficult to wrap your head around. Raymond's got it though - FTL machines (without any special frame of reference) = time machine. Stephen Baxter's Xeelee Sequence books have this as one of the key plot points several times.

Damnations!I wrote avery long post and Blogger just swallowed it.In resumé:FTL travel with FTL communication (special relativity handwaving):Whatever happens, you'll be in touch with the present present so whatever you know in the local future past is not of interest.FTL travel+STL communication:Great! You're in last 2012 four years of travel later. But your message to sell stocks will be eight years old by the time it will arrive at destination, in other words, four years AFTER you left.Useless. This is why I try and think of spacetime as local bubble of influence, the outside world lagging behind FTL-wise, but far ahead once we try and communicate with it.

On space monsters: You could still have a spirit world type of FTl, but the best way to avoid references to 40K is to treat it realistically: it's just going to be empty space (depending on author) incomprehensible to us/just too damn boring to be anything special.Otherwise, if you insist on spirit-world inhabitants, you should consider the possibility of mixed reactions within your crew.Christian reactions would go: AAARGH I'm in Hell and they're Demons! a Muslim xould exclaim: Djinns! and someone atheist could simply remark that we've encountered xenolife.

Looking the other way at STL; the only way you could have any sort of unified society, much less an Empire, would be to assume some sort of static culture such as ancient Egypt.

This might still be true with wormholes, especially if wormholes are very expensive to create/maintain. Wormholes go the key systems and STL branches out to nearby star systems from the terminus.

The Orion's Arm website has a great deal of explanation for how wormholes are thought to work in a consistent manner, I invite readers to check that out and see if that speculation makes sense or fits in with the underlying assumptions of "your" universe.

You could still have a spirit world type of FTl, but the best way to avoid references to 40K is to treat it realistically: it's just going to be empty space (depending on author) incomprehensible to us/just too damn boring to be anything special.

The kind of cosmic monsters I'm thinking of are with life cycles we might not even recognize. They're not space whales or space squid. It's going to be freaking alien, "Colour Out of Space" alien.

http://en.wikipedia.org/wiki/The_Colour_Out_of_Space

I've already mentioned the Dragons from the pinlighter stories.

In the hyperspace I'm imagining, we can't actually see it. The ship is encased in a hyperfield put out by the hypersails. It drifts along with the hyperspace medium. Moving up and down hyperspace clines will allow movement that corresponds to three dimensional space since the different clines move at cross-currents. The hyperfield can detect waves in the hyperspace medium and thus a sort of echolocation provides a sense of the surrounding environment. A starship navigator reads the waves the way a the Polynesians did, figuring out what's out there. He has charts from other ships that have traversed the area to provide some hint of where he's going but he's otherwise blind. Nobody can see what's on the other side of the hyperfield. You can push a camera out but the matter comes apart at the atomic level, like all the forces just stopped working and the atoms fall apart. You pull back a stump. So while there's something out there in hyperspace, you can't see anything. There's not even any sense of what the hyperspace medium is. Is it matter, energy, or space? Is it nothing like any of that? Are you pushing against something or nothing? Is it just fields? Fields of what? It's not exactly energy. You don't know. It's impossible to ever know because you can't sample it, you can't analyze it. You exist in a bubble of realspace and if you ever lose the hyperfield you will instantaneously cease to exist.

Navigators work around this blindness by augmenting their sensorium with a sort of synesthesia where the ripples against the hyperfield maps the data to their senses: sight, hearing, taste, smell, and touch, temperature, kinesthetic sense, pain, direction, balance and acceleration. Each navigator will perceive hyperspace differently and the particular idiom their subconscious chooses for experiencing it will translate to varying abilities.

So for a cosmic monster living in hyperspace, there's nothing much that can be known for sure, just speculation. It's not another human ship. It's capable of moving within hyperspace, up and down clines and even pushing against the medium from within a cline. All that's known is that they will attack ships when they come near. Is it a territorial display? Do the human ships look like food? Are the hyperfields "noisy" for the medium and simply bother the monsters? Are the monsters alive? Does that have any meaning in any context that would make sense to us? Do they eat, reproduce, have even the slightest similarity to realspace lifeforms? It's impossible to study them. All that's known for sure is they will charge at human ships and try to destroy them. Direct collisions will see their bulk push through the hyperfield and do something that removes both from existence. No one is sure what happens inside the hyperfield during a collision since the only people to have seen it from the inside died immediately thereafter. More cagey monsters will try to cross the ship's path with its own wake, creating a turbulent condition that will force the ship to translate back to realspace to avoid sheering the hyperfield and consequent destruction of the ship.

Now it might be interesting for them to not all be hostile. Perhaps only a portion of them are and others will drift near the ship and then drift away. Some of them could be truly huge, dwarfing the ship by a significant amount.

The best part of all this is, because you can't actually see these things, can't touch or examine them, they will remain as alien as could possibly be.

"Say a wormhole is created, and one end sent off towards Tau Ceti at sufficient velocity for a dilation factor of 0.1. When observing the far end on its travels from Earth, it would appear to take just over 30 years. For an observer traveling with the far end it would take 3 years. An observer looking through the wormhole on Earth, however, would also see the journey take 3 years."

Uhhh...sorry, no. What a person at the origin would see peeping through the wormhole is everything at the other end taking ten times as long to transpire. Relativistic time dilation is not time travel. It's clock slowing, that's all.

WRT "rest frame", that's just shorthand for "the guy travelling at such a significantly lower velocity that he might as well be at rest".

"Uhhh...sorry, no. What a person at the origin would see peeping through the wormhole is everything at the other end taking ten times as long to transpire. Relativistic time dilation is not time travel. It's clock slowing, that's all."

Uhhh...sorry, yes. According to the guys and gals who actually work with GR and tensor calculus (IOW way above either of our pay grades in the math department).

The wormhole solutions we've found under GR have all indicated that the two ends of the wormhole are at rest with respect to each other. Which means that observers not looking through the wormhole see the time dilation, and those looking through the wormhole see none. It's the difference between these two paths that results in time travel.

Also remember that GR doesn't just mean "clocks slowing". It also means distance compression and expansion (depending on relative velocity) and our concept of simultaneity breaking down.

What you describe is what would happen if there is a special reference frame for wormholes. Given what we know of GR, and how little we know of quantum gravity, there isn't (so far).

Ferrell:

None of the effects of GR are "apparent" or an "illusion". All the effects are equally true. GR results in the effects themselves actually being different depending on the observer.

Uhhh...sorry, yes. According to the guys and gals who actually work with GR and tensor calculus (IOW way above either of our pay grades in the math department).

The wormhole solutions we've found under GR have all indicated that the two ends of the wormhole are at rest with respect to each other. Which means...

...that you couldn't move one wormhole mouth without causing the other to follow. Or that information cannot be transmitted between wormholes moving with respect to each other. Either would preserve causality, but make wormholes useless. Presuming wormholes have a practical use, you have to presume that there's a causal disconnection between the two mouths. IOW, to even have this discussion, one has to presume the physicists are missing something.

It means the appearance of distance compression from a significantly slower moving reference frame. Aboard the relativistic ship, all distances are the same as always.

"What you describe is what would happen if there is a special reference frame for wormholes. Given what we know of GR, and how little we know of quantum gravity, there isn't (so far)."

Actually, I have a suapicion (though I don't have the maths to prove it) that all of this wormhole time travel comes from presuming that there are different reference frames. If one expounds the bounds of the reference frame to encompass everyone observing the exercise, everything happens in the proper order. That doesn't mean a special reference frame, just defining the "local" reference frame to incorporate all events of interest.

"...that you couldn't move one wormhole mouth without causing the other to follow. Or that information cannot be transmitted between wormholes moving with respect to each other."

No to both counts. The mouths are at rest with respect to each other through the wormhole. Surrounding spacetime is as per normal.

"It means the appearance of distance compression from a significantly slower moving reference frame. Aboard the relativistic ship, all distances are the same as always."

No, actually it's length compression of the moving ship for the "at-rest" POV, and distance compression in the direction of travel from the ship's POV. That compression of distance is the other way of looking at the time dilation.

"If one expounds the bounds of the reference frame to encompass everyone observing the exercise, everything happens in the proper order. That doesn't mean a special reference frame, just defining the "local" reference frame to incorporate all events of interest."

Can't do that, at least not in the way you're thinking. That was the entire point of GR.

Things only happen in the "proper" order if you're an observer outside the universe which can observe all points simultaneously. That's the special reference frame. That's also the usual description of hyperspace.

Okay, what if we agree to drop causality? I mean, sure, it creates paradoxes, but you get weird quasi-paradoxes out of quantum physics, too. Maybe our simple linear-causality brains just have trouble understanding.

(No, I don't actually believe this, but consider it for fictional purposes.)

"No to both counts. The mouths are at rest with respect to each other through the wormhole. Surrounding spacetime is as per normal."

Then you can't communicate information between the mouths without violating causality, because there is no reference frame in which one mouth is not moving WRT the other.

"No, actually it's length compression of the moving ship for the "at-rest" POV, and distance compression in the direction of travel from the ship's POV. That compression of distance is the other way of looking at the time dilation."

Sorry, but that's a naive interpretation. The clock-slowing interpretation is the one used by physicists like Leonard Susskind and Stephen Hawking. Following some odd, inexplicable impulse, I think I'll go with them.

"Can't do that, at least not in the way you're thinking. That was the entire point of GR."

General relativity is a theory of gravity. Motion induced time dilation is a consequence of special relativity. And, strangely enough, it is observer invariant. If you're moving in the relativistic spaceship, the people back at home appear to be the ones who's clocks are moving slower.

"Things only happen in the "proper" order if you're an observer outside the universe which can observe all points simultaneously. That's the special reference frame. That's also the usual description of hyperspace."

The arrow of time points in only one direction. All things happen in a definable order. It's only one's point of view that changes apparent order. If one could boserve all events from a point (even a moving point), and one knew the distances at which the events occurred, one could reconstruct the order of events, even if one sees them out of order because of lightspeed limitations on the propagation of information. No special reference frames need apply.

Two things have to be moving at the same speed in the same direction (i.e. at rest with respect to one another) in order to be sharing an inertial reference frame. You can't just define things as being in the same frame for convenience.

I can't really wrap my brain around it, but as I (fail to) understand it time connects different areas at different rates, so to speak, depending on how fast you are going (i.e. what angle you are moving in space-time - you are always going forward in time, so when moving in space you're going diagonally - or something).

Imagine trying to explain geometry to a hyperspace demon with no concept of space:

"You're trying to tell me that something that's 30 feet forward and 40 feet to the left is only 50 feet away? That's absurd! You are still going 30 feet + 40 feet = 70 feet. It must be an illusion. Your measuring rods may be measuring the distance as 50 feet, but the REAL distance is still 70 feet!"

If you look at two trees from one angle they are right in line, from another the pine is to the right of the fir, from another the pine is to the left of the fir. Are they still in the same places? Yes. Is this an illusion? No, it's perfectly real. Is there some sense in which the pine and the fir are actually ordered in one way or the other? No. It's relative.

jollyreaper said:The kind of cosmic monsters I'm thinking of are with life cycles we might not even recognize. They're not space whales or space squid. It's going to be freaking alien, "Colour Out of Space" alien.http://en.wikipedia.org/wiki/The_Colour_Out_of_Space

That was from 1927. Lovecraft had an even better analogy in 1920 with his From Beyond. These inconceivable horrors were actually in an alien overlapping reality, i.e., a "hyperspace".

More recently was a nasty little novel named "Stardeath" by E. C. Tubb.

Tony:Uhhh...sorry, no. What a person at the origin would see peeping through the wormhole is everything at the other end taking ten times as long to transpire. Relativistic time dilation is not time travel. It's clock slowing, that's all.

I'm afraid that turns out not to be the case. Hard SF author Stephen Baxter used this in his novels.

Take a wormhole, which has Mouth A and Mouth B. Leave Mouth A in Earth orbit. Attach Mouth B to a relativistic starship. Boost the ship up to a gamma high enough to show relativistic time dilation. Take the ship on a leisurely round trip cruise, eventually returning to Earth.

Now, if you jump through Mouth B, you will instantly appear at Mouth A, but in the past by an amount equal to the total time dilation. And jumping through Mouth A will send you into the future by the same amount.

Yes, as mentioned in the website that Rick helpfully linked to, the deal is "Causality, Relativity, FTL travel: chose any two." You cannot have all three. Unless you use the loop-hole (see below)

So dumping Causality is a solution to the problem. Whether an SF author wants to deal with implications is another matter.

The loop-hole is postulating some law that will prevent time machines from causing temporal paradoxes. This breaks the chain.

You cannot have all three because: Relativity implies FTL = time machine, time machines can cause temporal paradoxes, temporal paradoxes destroy causality. But if you prevent time machines from causing paradoxes, the chain is broken, and SF authors can rejoice.

And the four main ways of enforcing a no paradoxes clause are Parallel Universes, Consistency Protection, Restricted Space-Time Areas, and Special Frames. Most of which have already been mentioned. Special Frames has the drawback of being forbidden in Relativity.

I haven't even had a chance to read this thread yet, but Blogger is definitely throwing comments unfairly in spam jail, and there were also a spate of duplicates (which I left in spam jail, though they aren't actually spam).

Ok, I conceed that time travel via wormhole is possible; until we actually discover or create one to test the theory, I'll still have doubts but will admit to it being true as far as we know. However, I do have another question about wormholes: are wormholes made out of "stuff", or are they topographical features of space-time? In other words, can you move them? A tunnel is the absence of earth and rock; while you can move the stone, brick, and concert that defines the tunnel, you can't move the absence of subatance itself. If wormholes are the absence of distance between two points, then how do you move that absence of distance? The only way I can think of is by direct manipulation of space-time itself; and at that point, you don't really need wormholes, do you?

I've read a lot of Baxter's work. I'm not wholly convinced he got the implications of wormholes right. Here's the problem, as I see it (and we should answer Ferrell's question along the way):

A wormhole is a topological phenomenon, connecting two points in spacetime, but not through spacetime. But it's mouths have to be causally connected to matter (albeit exotic matter) in spacetime in order to stay open, and for the wormhole to be traversible.

Now, we are told that the two mouths are both in the same reference frame. If you move one mouth, then you automatically drag along the other and it's spacetime matter anchor, in order to keep the whole thing in the same reference frame.

Or you don't, in which case you put the two spacetime anchors of the wormhole mouths in different reference frames. That implies an interface between the anchor reference frames and the wormhole reference frame. What happens there?

Or it doesn't imply anything like that, in which case the wormhole mouths are in different reference frames, and those frames intersect at some point "inside" the wormhole.

Or they don't. In which case each mouth reference frame has to intersect with an "inside" reference frame (WRT the wormhole).

Or the wormhole, mouth's included, are all in the same reference frame. Rinse, repeat.

Are we seeing the problem here? The wormhole can't be divorced from spacetime or spacetime inertial reference frames. But to move the mouth's independently, you have to establish a different spacetime inertial reference frame for each mouth, because each mouth has a causal connection to the spacetime in which it is opened.

"However, I do have another question about wormholes: are wormholes made out of "stuff", or are they topographical features of space-time?"

Short answer: both.

Long answer: we're not quite sure, since we don't have a theory which connects general relativity and quantum mechanics. It's the same problem we have with black holes and singularities - black holes are made of matter/energy, which is what gives spacetime its curvature, but we're not sure where the black hole stops and the singularity beings. In somewhat more mundane terms, a black hole (and by extension a wormhole, which is a similar matter/spacetime configuration) can be treated as a discrete astrophysical object. It has a finite mass, it radiates a finite energy (as Hawking demonstrated, and as we're finding more evidence of), responds to other gravitational influences, has angular momentum, and can even have charge.

TL;DR answer: it's a topological phenomenon created by a certain configuration of stuff. Move the stuff around, and the topology goes with it. We think.

Tony:

"A wormhole is a topological phenomenon, connecting two points in spacetime, but not through spacetime."

There's the problem. A wormhole connects two regions of spacetime with an interconnecting region of spacetime (current GR wormhole solutions indicate this region is flat spacetime, ie non-curved, ie the ends are at rest wrt each other through the wormhole). It therefore can be considered to exist in two frames of reference simultaneously: around, and through. The "through" frame is between the wormhole ends, and is static. The "around" frame can change.

jollyreaper:I like your dark hyperspace. If you allow for mysterious forces that can block travel you can preserve causality (and explain by not explaining any number of things that would otherwise not make sense). FTL reconciled with Einstein by unfathomable divine intervention.In Stardeath, a wreck is found. How boring. But if you don't find wrecks, how do you know the ships lost in hyperspace are destroyed? Their crew could be alive "somewhere". What proof is there that your hyperspace monsters aren't just a story made up by navigators to steal ships? And who'd believe a gal who says she's been abducted by the hyperspace beings and has a message for humanity?

Thucydides:The whole culture needn't be so stable. You don't need dynasties of theocratical monarchs. You only need the part of the culture that's concerned with interstellar travel and the force that keeps the empire together to be very stable. A guild of sorts could do it for instance.If interstellar engines and fuel double as a WMD (how would they not?), you have an incentive to keep the people handling the stuff very predictable and shielded from the squabbles of the plebs. Whoever controls the WMD can then threaten their planet-bound brethren into submitting to their conservative decrees and paying tribute. Once you have several planetary systems, you can afford to lose one to make a political point...If there's only a small amount of interstellar travel, planteary systems could be basically autarchic and mostly free while a single interstellar organization wields the ultimate power in every system. A virtual monopoly on interstellar travel is menacing enough in its own right: take out the local Ad Astra Orientis chapter and have the last three generations of your people orbit powerlessly around their star while the arm of vengeance heads towards them.

By the way: any astrophysics geek knows if there's anything that would prevent a bunch of stars from being *much* closer to each other than is typical in this part of the galaxy? If you really want a plausible setting with resonably fast interstellar travel without spookiness, that could be the ticket.

I think that the time dilation only occurs if you ACTUALLY move at relativistic speeds. And where time travel happens is where your speed is faster than light. So the trick is to effectively travel faster than light without actually moving faster than light. This involves the warping of space itself to make things closer. We've seen evidence that space itself is expanding, welling up from vacuum energy or something. In fact, it is expanding at a rate faster than light. We've also got theories that mass bends space, which explains gravity. So space is malleable, we just need science and technology to figure out how.

Once you accept malleable space, you can do stuff like bend it back on itself and jump between the two points. That's basically a wormhole. Another possibility is collapsing the space in front of you and then passing through the space slowly, then letting it expand again behind you. That is essentially a warp drive.

Someone brought up Lovecraftian horrors... I like the idea of enslaving one of them for its reality warping abilities and then amplifying and directing that ability as a means of propulsion.

i've got a writeup on my hyperspace concept if you'd like to see it. I'd say it's at the end of the first rough draft. Now it's time to shop it around and see what holes can be poked in it. A couple of caveats:

1. The idea is trying to reconcile romantic notions of space opera with something that gives more than a passing nod to plausibility. Your disbelief should be gently suspended, not hanged by the neck until dead.

2. I'm trying to get the most mileage out of the least amount of assumptions. Don't throw in artificial gravity and intertial dampeners if I can get away with reasonable reaction drives for sublight maneuvering. People can spin parts of the ship if they want gravity.

3. Trying to avoid coming up with "steam galleys." (using a steam engine to power banks of oars when a proper screw would make more sense. Gloriously and extravagantly inefficient, that's the kind of fail I'm trying to avoid.) You could also define this brain fart as the mechanical horse drawing a carriage when it would be easier to just make a freakin' automobile. Also an example of the diamond monomolecular blade. Yay, you used clarketech to create the ultimate sword. Your ass will be handed to you by someone with a flintlock rifle.

4. Accepting that people may or may not like the premise itself. That's not important. What's important is if people who like the premise can still poke holes in it. That means there's more work to be done.

So, I've got the whole writeup in google docs. If you're interested, I'll add you as a reviewer. Just provide an email.

To whoever said "Someone brought up Lovecraftian horrors... I like the idea of enslaving one of them for its reality warping abilities and then amplifying and directing that ability as a means of propulsion."

Your stardrive is a demon in a bottle? That's different...

Thinking about wormholes makes my head hurt. Warp drives are only a little better. The theory that there are 'left-over' dimensions that you can inflate through the proper application of energy and then use them to bypass distance is intriguing, but of lower probability than creating artifical wormholes. For story purposes, I think I'll stick with either biofeedback controled hyperspace drives or the Zoom-a-tron(tm) unfanthomable stardrive. More plausible stardrives seem to involve millions (if not billions) of tons collapsed into the volume of a pea; or the use of tunnels in the sky that take centuries to build before you can use them. A starship the size of a city or a 1950's style rocket ship with a celestial doorbell...we should be able to figure out something between those two extremes.

The problem with a wormhole network that has no cycles and in which it is impossible to add new wormholes between already visited worlds without causing a temporal paradox, is that some sort of disaster destroying or making inhospitable even one of the wormholes in your network would cut your civilization in half, permanently, with no ability to reconnect it.

There is also the issue that as increasingly more places are connected by wormholes and thereby "banned" from ever charting a tramline through again, space will start to look quite hazardous and difficult to navigate when trying to plot new wormholes. Just what are the implications of permanently damaging the fabric of reality in this manner?

Rick:

"The alternative, so far as I can see, is simply blowing off a lot of well-establish physics entirely."

Actually, all you need is some universally preferred reference frame, which could prevent all temporal paradoxes from occuring. Fortunately, a universally preferred reference frame already exists and is known by modern science.

Namely, comoving coordinates. Yes, yes, I know, General Relativity says that no inertial frame can have a priviledged status. The key thing is that comoving coordinates are not an inertial frame. That is, they are not a "frame" in the sense defined in special relativity. Specifically, two objects could both be considered to be at rest in comoving coordinates, while still being relativistically considered to be moving away from each other (due to the expansion of the universe). Comoving coordinates can be associated with a local inertial frame at any given point, but these will be different frames for different points. Nonetheless, comoving coordinates are well-defined in terms of our current cosmology, and are empirically verified to be meaningful: most matter in the universe has a low "peculiar velocity", which is the name for an object's speed relative to what comoving coordinates consider to be "at rest" in an absolute sense. (By "low", I mean "less than one percent of the speed of light". This is still faster than the fastest man-made object built to date. A torch engine or Bussard ramjet accelerating at one gravity for not much more than a day should be enough to match these speeds, though.) Thus, if you want faster-than-light travel that's marginally consistent with relativity, then comoving coordinates are the way to go. Of course, even with comoving coordinates, no current physical principle is known that would allow you to makes use of them for FTL travel. You're still going to have to make something up for that.

Mind you, if the universe were not expanding, then comoving coordinates would be an inertial frame. However this is most likely meaningless, since comoving coordinates are defined in terms of Big Bang theory, and a non-expanding universe could not have come into existance by a Big Bang. In any case, this would still not violate relativity, because relativity never says there cannot be a preferred frame. It merely states that it does not know of any way to determine a preferred frame. Scientists don't much like choosing a frame completely arbitrarily, so they'll look oddly at your story if you don't justify why you picked the frame you did. But it's perfectly possible to have a frame coming from some other theory besides relativity, as long as it doesn't feel "arbitrary".

"Otherwise, if you insist on spirit-world inhabitants, you should consider the possibility of mixed reactions within your crew.Christian reactions would go: AAARGH I'm in Hell and they're Demons! a Muslim xould exclaim: Djinns! and someone atheist could simply remark that we've encountered xenolife."

So what are these beings like? A major tenet of Islam is that djinns have free will, like humans, and are capable of choosing good or evil. While djinns are seen as incredibly powerful and dangerous, they are not purely malicious or impossible to reason with. (And even in Christian theology, demons are fallen angels, and so could theoretically choose to repent - although all demons have per definition chosen to do evil at some point.)

Jollyreaper:

"The best part of all this is, because you can't actually see these things, can't touch or examine them, they will remain as alien as could possibly be."

We cannot see subatomic particles, but we still know pretty well how they work.

Tony:

"Actually, I have a suspicion (though I don't have the maths to prove it) that all of this wormhole time travel comes from presuming that there are different reference frames. If one expounds the bounds of the reference frame to encompass everyone observing the exercise, everything happens in the proper order. That doesn't mean a special reference frame, just defining the "local" reference frame to incorporate all events of interest."

This would mean that, once you have created a wormhole network in some frame, you cannot then create another wormhole in a different frame. This inability to create a wormhole in a different frame means that either (A) you have permanently ruined the fabric of reality, or (B) there is a physical law mandating which frame wormholes must be made in which is independant of how you chose to create your first wormhole, which means that there is a universally preferred frame.

Cambias:

"Okay, what if we agree to drop causality? I mean, sure, it creates paradoxes, but you get weird quasi-paradoxes out of quantum physics, too. Maybe our simple linear-causality brains just have trouble understanding."

The problem is that time travel is such a powerful ability that if it exists it will tend to dominate your story. Trying to include time travel in the background while keeping a society that looks mostly like ours will ring false.

I use "see" in the broadest term. What could you tell me about an animal glimpsed only briefly in a grainy video, one that is unknown to science? I'm sure you could make some educated guesses but any biologist would be much happier with a specimen to examine directly. Paleontologists are making due with something far less than table scraps looking at fossils.

Now take even the fossils away. You're seeing something with nothing more than hyperspace vibrations and even that has to be run into the sensorium via a computer. You have just enough resolution to tell a big blob from a little blob. And there's no possibility of retrieving a sample. There's no way to try to sample it in place within hyperspace.

The closest comparison you could make is to the cosmologists who are trying to put everything together through observation and modeling since they can't really create test universes to model their theories. The physicists can build particle accelerators but the cosmologists are out of luck. But at least they're living in the same universe, can work with the physicists on the little experiments and see if the principles discovered can be put in their models and explain the big picture.

The cosmic monster hunter is even more limited than that. He doesn't even know what the monster's made of. Maybe it's made of the stuff of hyperspace -- whatever that is -- or it's a creature that evolved in realspace and is using a hyperfield to encase a bubble of realspace,

So you might ask how a human ship looks different from a cosmic monster. It's like with radars in WWII, the operators could tell proper aircraft from the foo fighters. Alien saucers or transient atmospheric phenomenon, whatever those UFO's were, they didn't act like human blips.

"By the way: any astrophysics geek knows if there's anything that would prevent a bunch of stars from being *much* closer to each other than is typical in this part of the galaxy? If you really want a plausible setting with resonably fast interstellar travel without spookiness, that could be the ticket."

Stars have a much higher density in the arms proper, and even more so further in towards the core. There's also a number of nebulae with high stellar density. The problem is that higher stellar density means much, much higher incidence of extinction-level radiation events, making life that much more unlikely. Might be alright for colonization timeframes, but I wouldn't bet on any sort of native life (or useful atmospheres, for that matter).

Citizen Joe:

"I think that the time dilation only occurs if you ACTUALLY move at relativistic speeds. And where time travel happens is where your speed is faster than light. So the trick is to effectively travel faster than light without actually moving faster than light. This involves the warping of space itself to make things closer. We've seen evidence that space itself is expanding, welling up from vacuum energy or something. In fact, it is expanding at a rate faster than light. We've also got theories that mass bends space, which explains gravity. So space is malleable, we just need science and technology to figure out how."

Alcubierre drives are that same idea - problem is, unless they use a special reference frame you can still get time travel scenarios (less common, but the potential's there).

Other thing is, we're always moving at relativistic speed with regards to something.

Milo:

"The problem with a wormhole network that has no cycles and in which it is impossible to add new wormholes between already visited worlds without causing a temporal paradox, is that some sort of disaster destroying or making inhospitable even one of the wormholes in your network would cut your civilization in half, permanently, with no ability to reconnect it.""

Not true. You can rebuild the wormhole link which was destroyed, or bypass the system. As long as there's only a single link, you may end up even further in the future of the destination frame, but as long as you rebuild only the link which was damaged, you'll be fine paradox-wise.

"Comoving coordinates..."

...are a good candidate for a special frame for FTL, yes. The question comes in regard to quantum gravity - a fully-defined theory of quantum gravity would, if I understand correctly, quantize spacetime itself, and would have to choose between comoving coordinates as the quantized reference frame, or result in a preferred inertial frame. I could be wrong, of course, and anyone who knows more about candidate QG theories should certainly speak up.

Ferrell:

"Your stardrive is a demon in a bottle? That's different..."

It's certainly outside the usual hyperdrive handwavium. It would also lead to a merger of theology and physics, though...

Finally, a statement in this discussion that I can fully understand. (And agree with.)

I know causality is all tied up with the speed of light and the conveying of information but I don't feel it with the same intuitive sense of realities in the physical world like don't drop that glass, don't touch a hot pan, etc.

That sort of sums up the meta issue here, at least for me. I have a bias against occult/horror elements - for example, the Pirates of the Caribbean movies annoy me by dragging in the dead and all that stuff, when Errol Flynn and Maureen O'Hara managed to swash their buckles just fine without it.

Thus, I personally just want my damn ships to get around the human sphere on a time scale of weeks or months, with nothing lovecrafty about it, and the minimum graceful nod to violated laws of physics.

I do not claim this as anything more than personal bias, but I think it is something a good many people want, at least some of the time.

I'm in the midst of writing a story (it's satire) where the method of star travel is that a person uses biofeedback to control the trip through hyperspace; you use music to 'dance' the ship through hyperspace to your destination. The more skilled you are, the faster and more precise you trip through to your destiantion. The ship in my story has a third rate opera singer that does the 'navagation' by doning a biofeedback controller and giving a mini-concert.

I just have a really hard time even thinking through the logic of serious relativity puzzles and find it difficult to think of good stories to tell in it without being utterly confusing. Not to say it can't be done but I won't have anything useful to add.

Pirates bothered me by making very crappy sequels but original was great.

I think the biggest sin of genre mishmash is including ideas that aren't necessary. In pure and simple writing you have to ask if scenes are necessary, if subplots are warranted. Sometimes there's a bit of writing you're very proud of that simply must be discarded because it harms the flow of the story. You can really see this with cut scenes on the DVD for movies you admire. You can see how good the scene was on it's own and also why it was necessary to remove it.

So likewise with genre mishmashes, why are the elements there? Sometimes you just want flavor. A story of romance and betrayal could be told set in modern times right down the street but it feels more interesting in victorian England. Ok, that's fair. But you run the risk of taking too many side trips and losing the thread of the story. Now if the dynamics require class prejudice and scheming nobles and the potential for a man of humble origin to rise to great heights, now you have a real rationale!

The urban fantasy these days, the supernatural is brought in but not really used for much. It's much like the critique of poor scifi as space westerns where the trappings are worn less than authentically, more like drag.

A lot of those books annoy in that their characters are not up to the challenge and survive more by dumb luck and author fiat than anything else. It's hard to write a character smarter than yourself but it's no good avoiding it by writing an idiot instead.

Rick:With all the hypothesizing about FTL going on, why has no one focused on Heim Theory? IANAP, but if it is remotely within the realm of possibility you wind up with a fantastic twofer. You get an FTL drive and a reaction less STL drive. Yes, Heim Theory completely rewrites physics, but then we are talking science fiction. In the AIAA paper published by Droscher and Hauser in 2004, they broke down the physics, the theory as it applied to guidelines for a space drive, and gave an idea on power and design requirements. The longest story in the shortest possible amount of space, it gives you a drive capable of traveling within 10 light years in about 80 days. 34 days at 1g accelerating to a transfer into parallel space, crossing 10 light years in 11 days, then another 34 days decelerating into orbit on the other end. It gives you a travel time about the age of sail, makes the quickest communication route by ship (or mail packet), and allows for some close quarters combat around planets. It allows for drama and buckling of swashes in orbit, with your red haired hottie at your side.

"Thus, I personally just want my damn ships to get around the human sphere on a time scale of weeks or months, with nothing lovecrafty about it, and the minimum graceful nod to violated laws of physics."

But...but...Lovecraft is so much fun! (For certain values of fun.)

In all honesty, I don't mind the bottled-demon hyperdrive, as long as there are no goddamn psionics. Seriously, I hate psi-wank, especially as the key component of a technological artifact. Capture demons for propulsion with particle accelerators, not women chanting in Welsh.

Ferrell:

"I'm in the midst of writing a story (it's satire) where the method of star travel is that a person uses biofeedback to control the trip through hyperspace; you use music to 'dance' the ship through hyperspace to your destination. The more skilled you are, the faster and more precise you trip through to your destiantion. The ship in my story has a third rate opera singer that does the 'navagation' by doning a biofeedback controller and giving a mini-concert."

Two words: speed metal.

David:

I've mentioned Heim theory in passing before, if only because it reads exactly like the usual handwaved hyperdrive so many SF authors speak of. Cheap antigrav, parallel space, and links to vacuum energy - it's almost as if the whole thing were a large-scale punking of the physics establishment by a space opera fan. Not to say it is, or anything. It's just startlingly similar to common handwavium. I'd be the last to complain if it were correct.

One of the implications of Heim-Droscher theory (12D version) is that the universe is actually 10^127 years old, with matter appearing 15 billion years ago when metrons became small enough. That reminds me a bit of the Midfuture Religion thread, and the references to "formless chaos" being organized by god into the universe as we know it.

In all honesty, I don't mind the bottled-demon hyperdrive, as long as there are no goddamn psionics. Seriously, I hate psi-wank, especially as the key component of a technological artifact. Capture demons for propulsion with particle accelerators, not women chanting in Welsh.

@ Raymond -- what do you consider to be a classic example of psi-wank? Worst offenders?

Going back and reading the '04 Droscher paper again, I remembered that for a given strength of the "gravitophoton" field produced, there's an inverse relation between the gravitational field produced by the craft and the speed achievable.

- The Stars My Destination. I love the book to death, but there's always that wedge of impossibility.

- Ringworld. Luck? As a gene? Really? As a major plot driver? Really really?

There are others, of course, and off-the-cuff comprehensive lists aren't my strong suit. My usual problem is that whatever the psionic powers are, they don't tie into the physics anywhere else. 40K is actually the diametrical opposite of this, since everything about psykers is tied to everything else that happens, including and especially the very means of travel and the deadliest existential threat to the Imperium.

In all honesty, I'm just looking for an end result. I just need to cross the distance, and not have mad,insane, amounts of handwavium. I want room enough for a courier ship to jump from system to system, carrying essential messages like some futuristic Pony Express.

Having spent a few years as a freight dog in the civilian aviation market, I thought that applying some of that background to a future environment would make for some good storytelling.

I just could not have women singing in Welsh as they flipped tarot cards. Of course, I'm using something almost as far fetched.

In fact, given the realspace velocity to n-space velocity relation, you'd even have an element of skill for couriers. Plotting paths between systems so you spend the least amount of time in realspace, plotting courses which swing around planets instead of slowing down and changing direction, optimizing your loop to reduce the period, chasing lucrative work in disputed systems, riding the edge between realspace detection times and inter-system travel - sounds perfect for what you're doing.

Ok, I get what you're saying. In other words, telepathy is too much like magic for your taste. My initial reaction to seeing it in B5 was not liking it because it was seemingly a little too far-fetched for something trying to be scifi. Humans spontaneously evolved telepathy and it just showed up in the future? Smacked a bit too much like Marvel mutants showing up. Finding out that the Vorlons built it into us resolved that objection -- godlike powers meddling.

I have a general bias against unwarranted genre jumping. I can enjoy a spook story or hard SF or historical drama but I generally dislike it when a story jumps genres in a way that doesn't feel warranted. For example, the Postman was supposed to post-apocalyptic US of A. There was no need to work in genetic super-soldiers, changing the story from real world apocalypse to scifi apocalypse.

40K doesn't bug me as much in that regard because they expressly said from the start "tech and magic are here in this setting."

As for the Foundation, the whole premise of the story was predicated upon psychohistory which is a pretty big handwave to begin with.

How much did Dune bother you? The supernatural elements there remained mostly unexplained. The thing that stuck out for me was that there was plenty of religion without any indication of whether any of it was real, i.e. whether or not they had proof. I guess Herbert wanted to keep things as ambiguous as the real world.

The "singing in Welsh" thing is actually an example of the sort of thing that always bugged me with the depiction of magic. How's it supposed to work in a setting?

You have clerical magic where a supplicant asks a divinity to intercede. The divinity either performs the action itself or grants the power of magical action to the cleric. Ok, that works.

With the stirring of potions and the like it's just alchemy that actually works. Just like you get yeast involved in fermentation, you're mixing magic in with the components and there's a little magic in those things, too. Fine.

But what is it about hand motions and spoken words that cause spells to work? What is it with symbols like crosses making vampires flee? A lot of that stuff makes more sense if placed in the context of being human-designed magic systems. You create a servitor race, you don't want just anyone giving it commands. You implant behaviors in its mind so that it will obey warding sings. You create a powerful AI, you carry the token on your person so that it only obeys you. Or if you don't trust a key, you lock it to your own genome so that only you or a descendant can pull the sword from the stone -- er, give valid commands to the AI.

The scariest thing I could imagine is a legal system implemented by magic. When you are bound by the terms of the contract, you are really bound by those terms!

Actually, that brings up one of those wallbanger world breaker inventions common in scifi and fantasy -- the truth detector. If something like that really worked, if it couldn't be fooled by a sociopath, it would change EVERYTHING. Usually something like that gets used as a temporary plot device and forgotten.

I almost put it on the list. Dialing down the supernatural elements and visions of the future could've been done, frankly, without doing too much violence to the plot or characterizations. The Guild's navigators could've been a computational complexity thing. They basically were in the given explanations, but with a bit of actual seeing-the-possible-futures, and the latter could've been merely a factor of discerning potential scenarios, rather than actual prophecy. The Muad'Dib portion of the prophetic powers is harder to excise. I think it could be done, but not without softpedalling the crushing effect it had on Paul.

"The "singing in Welsh" thing is actually an example of the sort of thing that always bugged me with the depiction of magic. How's it supposed to work in a setting?"

"Magic A Is Magic A" is a principle I appreciate in any work (and half the point of this blog, methinks). In SF, though, you already have Magic A. It's called physics. Magic B, which is where psionics, magic, demons, and Lovecraftian entities live, intersects with Magic A at a number of points. You can either define Magic B well enough to carry the consequences and extrapolations, or you can merge it with Magic A. 40K takes the former approach, and does it well. For all its other faults, the later books in Card's Ender's Game series do the latter decently. (Please ignore all the myriad places where "aiuas" conflict with already-determined particle physics.)

Either way can work, as long as one is consistent - and has explanations why we haven't found it already, why certain phenomena don't happen in stars or black holes, and preferably avoids a violation of the mediocrity principle (as Milo mentioned somewhere, either here or the Empire thread).

Random note: For once, I would like to see a science fantasy setting that doesn't try to flavor its magic as psionics. Do the robe and wizard hat suddenly fall out of style once we develop high technology?

What I also especially dislike is psionic aliens. It seems like "give them psychics powers" seems to be the only thing many authors can ever think of for making their aliens, well, alien. It does not at all convey the intended message of "there are other paths a sophont species can take besides the one humans took", because you have to go and invoke magic to make it work.

Jollyreaper:

"I use "see" in the broadest term. What could you tell me about an animal glimpsed only briefly in a grainy video, one that is unknown to science?"

Not much. But I could try to develop a better video camera. You could declare by author fiat that this is not possible, but frankly if hyperspace cameras exist at all, then I find it far less believable that we can't make high-res ones, than that we can't make high-res ones yet.

Failing that, it should at least be possible to get more and longer videos, which is simply doing what I have already successfully done before, only moreso.

Your final defense might be that launching that many camera hyperspaceships into dangerous conditions would be too expensive. But doing ridiculously expensive things for the sake of scientific research is already the character of present-day space travel.

"Paleontologists are making due with something far less than table scraps looking at fossils."

And yet paleontologists are still working out extinct species' characteristics with remarkable detail. Granted, they have the advantage of having other, still-living animals that are similar enough to draw analogies to, so they have a starting point.

Raymond:

"Not true. You can rebuild the wormhole link which was destroyed, or bypass the system. As long as there's only a single link, you may end up even further in the future of the destination frame, but as long as you rebuild only the link which was damaged, you'll be fine paradox-wise."

"But what is it about hand motions and spoken words that cause spells to work?"

The hand motions would seem to be pushing against something. You know how by pushing up and down in a body of water you can create artificial waves? I imagine there is some sort of invisible aether that usually does not interact with our reality (like neutrinos), but that by pushing in the right patterns can be condensed into a form that has a tangible effect.

Okay, so that's a literal handwave...

"What is it with symbols like crosses making vampires flee?"

Well, originally, the idea was that crosses were a form of clerical magic. Vampires are contrary to God's plan, and so can be defeated by calling on his power.

Then some... okay, many... fantasy authors completely missed the point and included the "vampires are vulnerable to crosses" thing even in settings where Christianity is not objectively true.

"A lot of that stuff makes more sense if placed in the context of being human-designed magic systems."

Basically anything can be justified if you postulate "An intelligent designer with access to sufficiently advanced technology chose to make it that way".

But the thing is, let's say some important operation requires an overly long chant to activate. I am then not going to begin an extensive training program educating people to memorize the chant in question and recite it at high speed. Instead, I am going to reprogam my magic-producing tech to need a shorter password.

But...

Note that computer programming already looks quite a bit like magic to people who don't understand it. And, as Rick noted a few threads ago, to people who do.

The reason this works is because, even though we designed the details of the programming language, we are still constrained by the laws of logic and computation theory. Computer programs are not purely "passwords" to activate a hardwired feature - they in some very real sense actually describe what you are attempting to do.

So by the same token, a convincing language of magic should not simply have a password for "fireball" and another password for "teleport", but should actually describe reality in some sense, with open-ended capabilities in the hands of a sufficiently skilled user.

But also note that the programming is done more by the people making the computers than using them. If you want to launch a ballistic missile, you're not going to rapidly type up a guidance system by hand before enemy forces overrun you. Instead, you are going to take a guidance system someone else programmed, and simply press a button.

Jollyreaper:"3. Trying to avoid coming up with "steam galleys." (using a steam engine to power banks of oars when a proper screw would make more sense. Gloriously and extravagantly inefficient, that's the kind of fail I'm trying to avoid.)"

The paddlewheel steamboat is awfully close to being a 'steam galley'. Assuming some sort of FTL is possible the 1st FTL ships are likely to be weird kludges that attach the FTL drive to existing ship designs & only later is the equivalent of the screw propellor invented.

If there's one thing I hate about psyonics in certain sci-fi universes... its that they are made to be invincible, or better thn all the normal people in that universe, despite their technology. Jedi come to mind this late at night, but there are obviously others.

40K does manage to tone this problem down somewhat- they are powerful, but often can be defeated. The Mul in the Foundation series had some clear faults (I can't remember what they were but at the time that I read them, they were striking enough for me to have branded in my mind that he was not portrayed as overpowerful).

I forgot to sign my second comment. Sorry about that.The synesthesia in your FTL concept reminds me of a French sci-fi RPG by the way. Are you familiar with it? Maybe you pinched the idea from the same source as the authors. Their FTL was too spectacular however. Your concept sounds like it has the potential to be more believable (the less you show, the better I think). They brutally ruled out Milo's hyperspace cameras which seemed arbitrary while you could find another way, by making the hyperspace beings indistinguishable from the stuff of hyperspace itself. So are you correctly intuiting that "something is out there" like our ancestors deduced the presence of their predactors from the subtlest clues... or imagining something?You asked for an email. If my alias was Paul Atreides, it would be p.atreides@gmx.net.

I recall religions were explicitely man-made and not supernatural in Dune. And I thought the supernatural elements were explained (in as much as magic can be), with references to some of today's supernatural and pseudo-scientific beliefs. Maybe that's a semantics issue. I call the witches and the navigators supernatural. I call the jihadis and the Bible religion.

Raymond:

I thought the supernatural FTL in Dune was brilliant and ended up being more plausible than the physics-raping ad-hoc technobabble we're used to precisely because of how the actions of the prophets are constrained. It tells you: in this world, causality doesn't work like you or most characters assume it does. The future is not an epiphenomenon and fate (AKA consistency protection) is not just a fancy idea. As you note, you can't have Oedipus without an oracle anyway.But I didn't like very much the super-witches and their Hollywood-worthy antics. Much of that could have been dispensed with.

And why does high stellar density make useful atmospheres less likely?

Not much. But I could try to develop a better video camera. You could declare by author fiat that this is not possible, but frankly if hyperspace cameras exist at all, then I find it far less believable that we can't make high-res ones, than that we can't make high-res ones yet.

Referring to my previous paragraph:

Nobody can see what's on the other side of the hyperfield. You can push a camera out but the matter comes apart at the atomic level, like all the forces just stopped working and the atoms fall apart. You pull back a stump. So while there's something out there in hyperspace, you can't see anything.

I only used the camera as an example for terrestrial biology and if that's difficult with something on our own planet, imagine doing that for something in a different dimension! And you are correct, scientists can infer a lot about past ecosystems by looking at what's around today. But it was only within the last few years that we realized T-Rex would more than likely look like a deadly chicken, feathers and all.

I almost put it on the list. Dialing down the supernatural elements and visions of the future could've been done, frankly, without doing too much violence to the plot or characterizations.

I generally hate prophecy as a plot element because it's just so freakin' done to death. I know it's older than the hills and has been in stories both good and bad but I'm sick of it.

The only kind I'll allow would be one based on seeing possible futures. It's a branching of possible actions based on the mind-state of living actors. So the future will be shifting from second to second as resolve waivers and new feelings come into play. You're seeing the echoes of potential futures.

What got me thinking about that was playing a game of Lemmings years back. You could command detonate all your Lemmings when the game had become unwinnable. You get a five second count over all their heads and then BOOM! they all blow up. I thought "wouldn't it be scary to see a countdown clock like that floating over everyone's head in real life?" You see that person has decades, another person has a year, and the one you said bye to has twenty minutes. Car crash? Horrifying thought. You get to the airport and notice several people with 90 minutes left. You notice they're all coming to sit at your gate. Oh, crap.

The Muad'Dib portion of the prophetic powers is harder to excise. I think it could be done, but not without softpedalling the crushing effect it had on Paul.

I still wanted an explanation for how the genetic memory worked. It couldn't be passed literally in the sperm and egg. The mindspace must exist outside the body and the genetics is what allows you to access your own past selves. If it was in the sperm and egg, then you wouldn't know anything from those people after conception.

Actually, T. rex did not have feathers. Skin impressions have been found which show scales.

It did, however, evolve from earlier dinosaurs which did have feathers. It is believed that it secondarily lost them as it grew larger, because larger animals overheat more easily and so want less insulation. (Note how elephants have lost their hair.) It has been speculated that T. rex may have had feathers as juveniles which were shed as they grew, or that they had decorative feathers covering a few parts of their body which haven't been preserved.

Random note: For once, I would like to see a science fantasy setting that doesn't try to flavor its magic as psionics. Do the robe and wizard hat suddenly fall out of style once we develop high technology?

Here's an idea cobbled together from a few different sources.

Life asserts its own model of reality upon the universe. What we think of as constants in the universal and unchanging universe are so only because of life energy (we'll just call it the force.) When left to unthinking minds, which represents the preponderance of biomass in the universe, we see what we see. The thinking mind can act upon that and with an act of will fudge the laws, bend probability, make the impossible happen. When the act of will is done everything snaps back into place.

This is a variant on the "consensus reality" idea used in some settings.

Something that stories about prophecies generally omit is how the existance of prophecies changes what will come to pass.

I see it this way: if I prophecize a plane will crash, then I will warn people of this. (For the sake of argument, assume that the factual existance of prophecy is well-enough known that they actually believe me. No flat earth atheists, please.) But once warned of the crash, they can try to prevent it. Wouldn't that falsify the prophecy?

Some authors say that any attempt to prevent the crash is doomed to failure, since it has already been prophecized to happen. Other authors say that the prophecy only shows a possible future, and so it is still possible to make the future turn out entirely differently. I say that both of these authors are missing the point. I say that, in the scenario above, I will never prophecize a plane crash. Any timeline where I prophecize a plane crash leads to a temporal paradox as I work to cause my own prophecy to fail. The only outcomes I can prophecize are those which I find desirable, and those which are obviously beyond my power to change and would be so even without bringing in an arbitrary concept of "destiny".

The question is how would society be changed by the ability to stop plane crashes without doing a thing? (Okay, not quite - I might need to take action to ensure the plane's safe flight, but I will know exactly which actions to take, as I can predict the outcome of all actions and will only perform those which will actually work. So I don't need to think anything through, just mindlessly obey instructions from my future self - which my future self also didn't come up with himself, but simply remembers from when he was me.)

The synesthesia in your FTL concept reminds me of a French sci-fi RPG by the way. Are you familiar with it? Maybe you pinched the idea from the same source as the authors.

You neglected to mention a name but probably not. It was an idea that struck me from seeing Macross Plus where there was a thought-controlled transforming aircraft. People talk about making a vehicle an extension of your own body and I figured it would be interesting to take that phrase literally.

I recall religions were explicitely man-made and not supernatural in Dune. And I thought the supernatural elements were explained (in as much as magic can be), with references to some of today's supernatural and pseudo-scientific beliefs. Maybe that's a semantics issue. I call the witches and the navigators supernatural. I call the jihadis and the Bible religion.

Well, that's the part that threw me. I would tend to think that the existence of the supernatural would make religion hypotheses easier to take seriously. We know the Bene Gesserit cynically invent religions. We know that they were supposed to have had a part in shaping the religions the Fremen were inspired by but with mental superpowers, I was wondering if there really was supposed to be something to it. Ultimately I don't think there was, it's a godless universe with mental powers. But those were the questions i had when I first read it.

So by the same token, a convincing language of magic should not simply have a password for "fireball" and another password for "teleport", but should actually describe reality in some sense, with open-ended capabilities in the hands of a sufficiently skilled user.

It's interesting to point out the Dianne Duane's Young Wizard book series has magic that works that way. The 'words' of magic actually define reality, so you could, in theory, chuck a 6000K fireball down main street by defining it to be.

"If there's one thing I hate more than psionics, it's "wishing makes it so"-style magic."

What I really, really hate is "believing makes it so"-style magic. Particularly when it portrays flat earth atheist strawmen who don't believe in magic - and therefore successfully defy it - despite the obvious evidence of its existance. And when it never portrays people as recognizing the potential inherent in the system (I know that everything is possible if I believe in it hard enough... and since I believe in this, that means I can do anything).

"Wish" magic bothers me when it takes the form of Disney genie magic, where they have powers that somehow can't be used outside the context of a formalized wish from someone other than the genie. (This is totally not to be confused with mythological djinn, whose "wishes" were simply favors granted by the djinn, typically out of gratitude.)

What I really, really hate is "believing makes it so"-style magic. Particularly when it portrays flat earth atheist strawmen who don't believe in magic - and therefore successfully defy it - despite the obvious evidence of its existance. And when it never portrays people as recognizing the potential inherent in the system (I know that everything is possible if I believe in it hard enough... and since I believe in this, that means I can do anything).

The Matrix. When Neo finally truly believed in his own ability, he was able to basically become a god within the system. Ruined in the sequels, of course.

I've never been a fan of physical component spells or of the D&D system where the mage memorizes spells and the invocation of the spell erases it from his mind so he has to study it again.

Worse than that, though, are raw emotion powers. You get that in magic or in anything from Japan where the emotional state of the character determines the outcome of the fight. Most ridiculous in giant robot shows where sufficiently provoking the hero will allow his robot to suddenly defeat the bad guy. There was one show that actually tried to make that part of the premise, the robots are fueled by emotions. But for most shows there's no overtly stated magical connection, it's just ridiculous dramatic convention. Sort of like in American shows where a guy's getting pounded to hell and back, he should be at the point where he's just getting stomped on the ground but something happens to give him a second wind and he's now beating the hell out of the other guy.

If real life worked like that what you could do is take an orphan with cancer down to the track and tell his sister to bet her last dollar on the least likely horse so she can use the winnings to pay for his operation. There's no freakin' way that horse ain't coming in now. You make sure you put your own money down on it, too.

"I've never been a fan of [...] the D&D system where the mage memorizes spells and the invocation of the spell erases it from his mind so he has to study it again."

Oh right. Hate hate hate hate hate hate HATE.

Seriously, how stupid can a mage be to "forget" a spell after casting it once?

Yet despite how difficult these spells apparantly are to remember, you can keep them memorized all day, throughout numerous distractions, with no mental effort whatsoever. It's only casting them (an action that, as long as the spell is memorized, usually takes no longer than a few seconds) that actually makes you forget them.

"Worse than that, though, are raw emotion powers."

Hmm? I don't actually object to those. It's generally justified as willpower - people fight harder when they care really strongly about the outcome.

The raw emotion powers are usually employed outside of an expressly magical setting like in anime. Not talking about adrenaline boost like a motherblifting something heavy off her kid, it's like a pilot's plane flying faster because he's super-pissed now.

Raw emotion power can be ok if it's expressly magical like the Force but can become cheesy when the audience is watching the hero get pounded and just waits for the baffle to say something about the hero's mother so he'll go into berserker mode.

I did a setting where ships would enter into 'subspace' (never actually named it) by pinching off a bit of space around their ship. To the outside observer, it would appear as though the ship vanished off into the horizon, but it actually just shrunk down to subatomic size (in real space). That caused a hole in space which would then be filled with normal space producing a distortion wave similar to dropping a pebble in a pond. It would basically emanate out until it could ground out into a bit of matter (like a nearby ship, or a planet).

Once in 'subspace' its speed was limited by the gravitic distortions in the area (keeping in mind that the ship itself causes some distortions). In order to protect the ship, hydrogen gets injected into the bubble which then migrates to the perimeter of the field, where it slowly degrades and releases photons (probably only visible with special gear). Since gravity would pull disproportionately, sources of gravity would glow more brightly. So, to figure out where you are in 'subspace' you kind of felt your way through the bright spots. If you got too close to a gravitic distortion (i.e. a planet) your 'subspace bubble' would pop and you would re-enter real space at that location. Your inertia would sync up with the local gravity wave and a counter momentum wave distortion would then emanate out at the destination.

The point is that navigating in 'subspace' was much closer to dancing than mathematics. Also, your speed was much faster in the void between stars than within the systems themselves.

Remember that Dune was written in the 60's, when mind-powers and precognition had a little more scientific respectability. Herbert no doubt thought, as many people did at the time, that scientific proof of the untapped potential of the mind was just around the corner...

At least Dune deals with the causality-violating nature of FTL by making it integral to the plot (though I'm not sure if that was the author's motivation).

I must agree that "only humans with psionic powers can navigate through hyperspace" has been done way too many times and is far from hard SF.

I must agree that "only humans with psionic powers can navigate through hyperspace" has been done way too many times and is far from hard SF.

True. In my setting it's more like being really, really good at an art. There's no special genes involved or anything, it's just a matter of raw talent mixed with proper training. It's like being a good pilot or athlete or musician, not being a Guild Navigator. The difference between a good one and a great one can be summed up in Holmes' rebuke of "You see but you do not observe."

Why can't a computer do this? It's one of the fiats I'm throwing into the setting -- AI's max out as brilliant expert systems and can seem perfectly human but they just can't take the next step, they cannot attain true consciousness. It's the only way I can think of to avoid AI wank.

Another fiat is that there's only so far that can be gone with expanding a human mind until it collapses under the weight of its own overhead. You'll top out with brilliant polymaths and a few rare individuals capable of tightly integrating their own mind with a series of expert system augments but you're not going to see vastly superhuman intelligences, at least not among the ranks of the human populace. It's just too difficult to come up with stories that make a lick of sense in those settings.

The best idea I could come up with for what transcendent humans would be up to is running with the idea that human nature never changes. Removed from any concern from having to satisfy basic needs like food and shelter, with everything provided for them in their own heaven-like realm of existence, they end up concentrating on the most banal and esoteric bullpucky imaginable. I'm thinking of the struggling farmer scratching his head at the fads and scandals of the nobility, the blacksmith incapable of understanding why the theologian is wasting so much skull sweat on points of doctrinal differences that seem completely pointless and everyone gabbing about everyone else and being shocked and outraged over violations of court etiquette. Now just crank those trends up a few orders of magnitude and disgusted transapients who leave the culture will tell the normals "There's no way I could possibly describe exactly what's going on because the concepts are so difficult to translate but just accept that it's a bunch of pointless blather about nothing. And this is why I'm going off to study the ecology on this delightful little moon her and stay as far away from those insufferable people as possible."

Now in a standard setting, there should be no point of interaction between the high level transhumans and the normals. Normals have nothing they need, no resources, no means of aid, nothing. But if we were to come up with something the transhumans need, then the game becomes one of making sure those needs are satisfied and the transhumans remain occupied with their frivolities because if there ever becomes a time when scarcity returns, when there's no longer enough to go around and keep the transhumans happy in their little walled gardens, then you're going to see some heavy crap go down.

Following this line of thinking, that human nature never changes, Xerxes or Solomon or Washington would be in complete awe of the destructive power represented by nuclear weapons and would be more than willing to say that we have the power of the gods in this day and age. But when you tell them about the human failings that make nuclear war a possibility, they're back in territory they understand. The dumb reasons for going to war never change, just the amount of damage that can be done once the decision's been made.

The caveat to "human nature never changes", of course, is that once you start heavily genetically tweaking the brain, you're not exactly human anymore. It's possible for transhumans to become very, very different. So it's an author fiat in this setting that they aren't.

Slaves, experimental subjects, or pets. Those are pretty much the purposes for which we use animals today and in the past, so there's a precedent. (Also meat/body products, but there seems to be no good reason why products made from humans would be any preferable than other animals, unless the transhumans are sadists.)

You're right, I neglected to mention transhuman hobbyists. Orion's Arm has a lot of speculation in that regard as well as my question as to whether an upload would be the same. Is a huge philisophical question in that setting with many saying no, the upload appears to be the same but is just a really excellent duplicate. So if I have clone insurance and get killed, my me in my brain here is gone but the resurrected clone would be thinking "wow, I sure am glad I made it back in this clone body! I can see that was sure a nasty accident."

I think there's room for a whole giant pk dickensian story about the meaning of individuality when minds can be resurrected in clone bodies. I'm imagining a Titan if industry creating mind clones with the intention of trusting them as perfect co-CEO's and not thinking that he could ever be in disagreement with himself. But after the cloning each is a new mind experiencing the universe subjectively and may not reach the same conclusions. And after the original dies, the clones share his original drive to maintain a vision based on his burning desire but time could see each clone's shape of the vision change.

Perhaps the industrialist was warned of this in the beginning so seeks that each clone will be given the same information, will act as one. But he can't control everything. Love would be the cliched monkey wrench. I'm thinking some traumatic experience only one clone went through while the others did not. Maybe a near-fatal accident that gives that clone PTSD and he realizes the others do not share that event, that his experience is not theirs, and he appreciates how truly flawed his conception of immortality is.

So, tell me someone's already written this story. I'm sure they have and it was probably decades ago!

Slaves, experimental subjects, or pets. Those are pretty much the purposes for which we use animals today and in the past, so there's a precedent. (Also meat/body products, but there seems to be no good reason why products made from humans would be any preferable than other animals, unless the transhumans are sadists.)

But this brings up another question. Older scifi went with the idea of the godlike beings operating in physical realms, either on planets that were wholly under the dominance of their intellects or on ridiculously huge starships or in pocket dimensions walled off from our own. So it would stand to reason that if they wanted to play god to a planet of people, they needed a proper planet to play on.

The rise of the simulationist trope brings that into question. If it's possible to fully model the planet within a computer system, why go to the bother of creating it in the real world? We've already had that trend poking away at potential starship designs with authors suggesting disembodied brains or straight uploads piloting the ship with their physical environment being computer simulations with digital avatar bodies. The traditional starship is given an ear, turned on it, and then shoved out the airlock.

The only two reasons I can think of for that not to be the case: 1. There's some reason why they can't fully model everything in simulation space and need to do it for real in the real world. 2. Anti-simulationist bias which may amount to nothing more than personal aesthetic taste rather than for any practical reason.

The problem with #2 is that it reduces the significance of baseline humans to something less than a triviality. Which is ok if that's the kind of story you're trying to tell; if not, that's a significant problem to overcome.

Blogger's spam filtration is really struggling lately - I've had to let a bunch of real comments out of spam filter jail.

ISTR that one reason for the prevalence of psionics in golden age SF was that editor John Campbell was a zealous enthusiast of psionics, and so pressured writers to shoehorn it into their stories.

As for why particular chants or gestures matter in magic, my guess would be that this is ceremonial magic, which is in fact ... ceremonial. Whatever entity you are dealing with is responsive to things being 'done right,' or not.

I gotta say that if you must have magic in a setting, I prefer it to be magical, not simply mechanistic with different laws.

"Orion's Arm has a lot of speculation in that regard as well as my question as to whether an upload would be the same. Is a huge philisophical question in that setting with many saying no, the upload appears to be the same but is just a really excellent duplicate."

Now here's something to consider. Let's say that you one day wake up and find that there are suddenly two of you.

A discussion confirms that both of you have the exact same personality, memories, and body traits. There is no obvious way to determine which of you is the "original", since you appear to be identical down to the molecular level, or at least to the extent of accuracy that you can be bothered to measure.

Would you insist that there can be only one real you, even if you don't know which, and there appears to be no meaningful difference? Would you draw straws to determine who gets to keep your life? How would the other you feel about drawing the short straw?

"So if I have clone insurance and get killed, my me in my brain here is gone but the resurrected clone would be thinking "wow, I sure am glad I made it back in this clone body! I can see that was sure a nasty accident."

Or would that clone go "Wow, I'm glad that the real Jollyreaper (who is not me) saw fit to ensure my creation! I like my newfound existance! Oh, and I seem to have his memories, too.".

The thing is that immediately after waking up the clone would probably not realize it is a clone yet. It would just wake up in a lab with its last memories being when you had your brain uploaded. It would then have to either have the fact that it is a clone explained to it by the lab technicians, or it would have to reason this own its own based on it being the most likely explanation for the suspicious memory gap.

When informed that it is a clone, will it have a crisis of identity, panicking that it isn't who it thought it was? Or will it just consider itself the same person?

Also, something I suddenly caught: why am I drawn to using the pronoun "it" for clones? I would rarely use that for normal humans, even ones of uncertain gender. This is an odd subconcious decision considering that philosophically I do not believe that clones aren't real people.

Now consider something else. Many artists talk about "gaining immortality through their work". They feel that as long as they can successfully convey their ideas and emotions through their art, the most important part of them will not be forgotten, and their physical death, while regrettable, is an acceptable loss. Now add clones into the mix. If you see a value in gaining "immortality" by being remembered, then surely you would see even more value in gaining "immortality" by creating a clone who will remember everything you do, even if you do not believe that clone will be the same person as you. Perhaps the first thing your clones does would be deliver your eulogy from the viewpoint of someone better-placed than anyone to understand who you were.

"I'm imagining a titan of industry creating mind clones with the intention of trusting them as perfect co-CEO's and not thinking that he could ever be in disagreement with himself."

Hmm? I'm in disagreement with myself all the time.

"Perhaps the industrialist was warned of this in the beginning so seeks that each clone will be given the same information, will act as one."

If so, then they are no more effective at running a corporation than a single person. The entire point of having multiple people is that they focus on different tasks.

"If it's possible to fully model the planet within a computer system, why go to the bother of creating it in the real world?"

Immersion? Even if the actual world is identical, it's going to feel different if you know it's real and freed of any biases in your simulation model, and even more so if you're capable of personally walking among your pets. (You could upload your own brain into the simulation, or download the simulation as an illusion imposed on your brain, but do you want to do that? See above conversation on self-identity.)

Also, I think that accurately simulating a universe would require a considerably higher magitechlevel than merely having incredible control over the universe we already have.

Of course, if we accept the premise that full and accurate simulation of a universe is possible, then we have to accept the possibility that our universe is a simulation despite how real it appears. Therefore, simply saying that advanced civilizations would make simulations rather than bothering with real planets does not rule out worrying about us interacting with transhumans. In fact, since any civilization with simulation tech this good probably also has uploading/downloading tech, the identity of any given person as being "real" or "simulated" would be pretty fluid.

"The traditional starship is given an ear, turned on it, and then shoved out the airlock."

You shoved the starship out the airlock? I sense an interesting topological exercise. Maybe future civilizations discovered that the secret to FTL travel is Klein bottles?

"As for why particular chants or gestures matter in magic, my guess would be that this is ceremonial magic, which is in fact... ceremonial. Whatever entity you are dealing with is responsive to things being 'done right', or not."

But how does magic respond to things being "done wrong"? Are there spirits who take offense at your actions, or does an impersonal force go "Bad command or filename."?

There is always the possibility that the ceremonial parts of the spell aren't necessary, and are just added either because the wizard it just repeating tradition and honestly isn't sure which parts of the spell are actually necessary, or because the wizard wants to keep the ignorant masses guessing, or because it looks more awesome that way and wizards aren't usually humble, or just to let people know that a spell is being cast - if I see something suddenly explode, I would feel a lot better knowing that it was an allied wizard who zapped it, rather than an enemy wizard hiding around the corner.

In the original example, going from Sol to Wolf 359 would take you forward in time by about 9 years (since the distance is about 9 light years, and making various budget-cutting assumptions on the part of the tram-way builders). This would be called "coordinate time", as opposed to "proper time", which is how long the trip seems to you on the tram (and how much time your watch records as having passed). Going from Wolf 359 back to Sol would take you back by 9 years in coordinate time (but with a suitably small but positive amount of proper time for the trip duration). Similarly Sol to Sirius goes forward in time coordinates by about 8.6 years. So the trip from Wolf 359 through Sol to Sirius takes you back in coordinate time by a net 0.4 years.

If you open another tram-line direct from Wolf 359 to Sirius, you are perfectly okay as long as that tram passage also takes you back by 0.4 years of coordinate time.

If tram lines use wormholes, one way to ensure that everything works out in just this way is to make a wormhole pair at Wolf 359, then put one end in a box and pay the postage for shipment to Sirius via the tram-line route through Sol. Voila! Instant new line that takes you back exactly 0.4 years in coordinate time.

The drawback is that before the Wolf 359 to Sirius line, you had 7.7 years of slop in allwoing the time coordiantes to get out of synch (because, remember, that Wolf 359 and Sirius are separated by 7.7 light years). Once you open the new line, the tolerance becomes much closer - equal to the distance light takes to travel all the way through all three legs of the journey and return to where it started. So, for example, if all the Sol tram-lines connected to a Grand Central Station on Earth, passengers could just pick up their luggage and walk from one line to another. However, in order to keep Bad Things From Happening, the folks at Wolf 359 might need to keep their new line far from the terminals to the old line. For example, if they can tolarate a slop of 1 hour in time coordiantes, they would need to keep the distance from Sol terminal to the Sirius terminal in the Wolf 359 system plus the distance from the Sol terminal to the Wolf 359 terminal in the Sirius system more than a light hour. This might require getting on the torch shuttle to rocket across that light hour, making for a more inconvenient and expensive trip.

Someone with more time can verify this, but my understanding of semi plausible wormhole physics is that if two wormholes with different frames of reference are brought close to each other, they will create fields of virtual particles that will ultimately destroy the wormholes before the closed timelike curve can be established.

As I understand things, causality is maintained as long as you don't leave Wolf 359 before you left Earth, and you don't leave Sirius before you left Wolf 359. Given the slight relative proper motions of those three stars, that shouldn't be too tough a criterion to satisfy. The trick is expanding the frame of reference to include all nodes in the circuit, and not doing anything crazy inside that reference frame.

It is more complicated than that, since there is no way to determine simultineity. In other words, one observer might figure than in his reference frame you left Wolf 359 before you left Earth, and another would figure than in his reference frame you left Wolf 359 after you left earth, and both interpretations would be equally valid.

I have yet to see someone explain the causality problem with wormholes.

I have a wormhole. Going from wormhole end A to wormhole end B takes me from a coordinate time of t to a coordinate time of t - 5 years.

End A is located 2 light years away from end B. A light beam starting at end B will take 2 years to get back to end A. So going from end A to end B and sending a light-beam message back to end A will result in the message getting there three years before you started your journey. Since the effect (message reaches end A) happens before the cause* (leaving at end A) this violates causality.

*More precisely, the effect is in the past light cone of the cause, to use science jargon.

I will note that everything is in motion. Most things are moving dramatically different velocities. So if you open one end of a wormhole on Earth, and another on some planet on Tau Ceti, there will be a huge discrepancy in the conservation of momentum if anything passes through.

Not with wormholes. Momentum is always conserved locally with wormholes. If the wormhole end B has a mass of M1 before you go through and is initially at rest, it has no momentum in that reference frame. If you have a mass of M0 and you arrive going a velocity V, then after you exit end B that end will have a mass of (M1 - M0) and a velocity of -V * M0/(M1 - M0). Again, the vector sum of your momentum (V * M0) and the wormhole momentum ( (-V * M0/(M1 - M0) ) * (M1 - M0) ) is exactly zero. Momentum is conserved.

If you're going to have FTL, you're leaving behind objective reality as we know it.

I will point out, again, that wormhole geometries are allowed in general relativity, which is the best theory we have on space-time geometry. The necessary conditions that are required to allow wormholes to be stable (namely negative energy density regions of space-time) have been created in the laboratory.

they will create fields of virtual particles that will ultimately destroy the wormholes before the closed timelike curve can be established.

That's basically correct.

Correct as in 'established physics' or correct as in 'plausible and consistent with established physics?'

(I'm glad you dropped by, Luke, since it was your remarks on an earlier discussion thread that inspired this post. This blog is obviously speculative in nature, but in this case I'm in the awkward position of really not knowing what the hell I'm talking about.)

Actually, T. rex did not have feathers. Skin impressions have been found which show scales.

What that tells us is that Tyrannosaurus rex had scales, not that it didn't have feathers. Note that modern birds have both feathers and scales (on their legs and feet). It is quite possible that Tyrannosaurus rex had feathers on some parts of its body and scales on other parts of its body (and it is also quite possible that it had no feathers, or maybe quills related to feathers, or down-like fluff related to feathers - we simply don't have the evidence to say one way or the other).

Now here's something to consider. Let's say that you one day wake up and find that there are suddenly two of you.

That's a real toughie. I feel that the two would be diverging from the precise moment of copying. If it takes a day for the new clone to be brewed and decanted then the delta's already 24 hours.

Stross had this idea in Accelerando where post-humans would create ghosts of themselves to do tasks in virtual space. It's not just a visual thing like Dr. Manhattan in Watchmen where all of his sub-parts were controlled by the same mind. It's more like "Someone just mentioned something I don't know. Sub-me, go study it in accelerated time and report back to me." Sub-me's knowledge reintegrates with the primary personality so that it can be recalled with the same ease of having spent the time studying it himself -- because he already did in a way. If these ghosts accrued sufficient experience, they might consider themselves their own sovereign intelligence and refuse reintegration. Whole cans of worms to be found here.

Or would that clone go "Wow, I'm glad that the real Jollyreaper (who is not me) saw fit to ensure my creation! I like my newfound existance! Oh, and I seem to have his memories, too.".

That's just it. If we had a magic cloning box that duplicated me exactly, I'd walk in the one chamber with the other chamber being empty, the lights would flash and alarms clang and two of me would walk out. "Good, I'm the original!" I would think. Then the other me says "no, I am!" Well ok, which door did I go in because that's the one I came out! They both look alike. We'd go round and round.

The Orion's Arm philosophy of continuous death says that we're constantly changing states so we're constantly a different person from second to second, just that the changes are very minute on that scale. Take two clones forward a number of years and they'll be different.

So in a society with this sort of tech, I would imagine that there would be a religious fatalism about this sort of thing. A mind could splinter off a copy of itself to perform a kamikaze mission. The sub-mind knows the rationale of the original, will presumably still believe in it and might feel a sense of religious certainty about the death, the same way a martyr feels he's not reaching the end of one life but the beginning of another. The sacrificial mind might not see itself as dead, just a tiny part of it is dying while the rest continues.

A full clone of the mind might consider that subjective experience is the only way a mind is built and the merging of itself back into the parent mind is not death since those experiences will become a part of the mind and inform its actions.

So a mind might clone pieces of itself to send off to distant stars and integrate those experiences every few decades so it can keep abreast of what's going on. And yes, you then get to the thought of a transapient mind making a human copy of itself to live amongst us, experience our lives, impart lessons to then return after death for reintegration with the parent mind. (blasphemy alert!)

Now consider something else. Many artists talk about "gaining immortality through their work". They feel that as long as they can successfully convey their ideas and emotions through their art, the most important part of them will not be forgotten, and their physical death, while regrettable, is an acceptable loss. Now add clones into the mix.

That's what the industrialist could be going for, considering the clones to be an insurance policy that his will is carried out after his death. Who better to safeguard his interests than someone who feels exactly the same as he? Several someones.

"I'm imagining a titan of industry creating mind clones with the intention of trusting them as perfect co-CEO's and not thinking that he could ever be in disagreement with himself."

Hmm? I'm in disagreement with myself all the time.

That would be the obvious flaw in the plan. I have a feeling he might call it the Babel Project because religious groups would see his death-cheating as an affront to God and he would relish making it all the more overt. But the flaw would be that he can't count on his clones never changing their minds.

I think that he would ultimately prove unsuccessful. My thinking is he gets his brain read -- early attempts will be destructive and so he dies in the process. His mind is dumped into several clones aged 18 years. He bought legislation to make sure they could be his legal heirs. The tech isn't there yet to run his brain in a box.

By the time the tech gets there, it's a few decades later. His original mind is revived inside the computer and he gets to see how badly he misjudged. Well ok, how about I run it as a virtual person now? Can't. You're not legally a person, you have to be alive. And you don't have the money to buy the legislature this time, your company has lost too much power and influence.

In fact, since any civilization with simulation tech this good probably also has uploading/downloading tech, the identity of any given person as being "real" or "simulated" would be pretty fluid.

Right. Imagine the danger of having one of your backups stolen. It could be run in a sandbox with the thieves trying to influence you to divulge important information. Part of the training for any person important enough to be backed up is learning how to recognize simulated environments. Sort of like the area covered by Inception but that movie sinned by being dreadfully boring despite all the shooty s'plosions.

The other angle is that the backup is the person. Fire him up, let him live a little in virtual, then drop the bomb -- you are not you, you are the backup. We can give you a real body and let you loose in the real world if you do X for us. Do you trust them? Will you be willing to betray yourself?

Anyway, to really bake your noodle:

http://www.bottomlayer.com/bottom/argument/Argument4.html

This paper surveys evidence and arguments for the proposition that the universe as we know it is not a physical, material world but a computer-generated simulation -- a kind of virtual reality. The evidence is drawn from the observations of natural phenomena in the realm of quantum mechanics. The arguments are drawn from philosophy and from the results of experiment. While the experiments discussed are not conclusive in this regard, they are found to be consistent with a computer model of the universe. Six categories of quantum puzzles are examined: quantum waves, the measurement effect (including the uncertainty principle), the equivalence of quantum units, discontinuity, non-locality, and the overall relationship of natural phenomena to the mathematical formalism. Many of the phenomena observed in the laboratory are puzzling because they are difficult to conceptualize as physical phenomena, yet they can be modeled exactly by mathematical manipulations. When we analogize to the operations of a digital computer, these same phenomena can be understood as logical and, in some cases, necessary features of computer programming designed to produce a virtual reality simulation for the benefit of the user.

This is kind of on the level of the wormhole discussion for me -- not quite sure I'm following everything but the brain hurt is an interesting feeling. :)

I'll try to compress an answer to many of your questions about wormholes into one post.

(P.S., to forstall any questions I'll just state my qualifications - I am a Ph.D. physicist who studied General Relativity as an undergraduate and in grad school, although it is not what I work on in my professional career. I have also read Matt Visser's book "Lorentzian Wormholes: From Einstein to Hawking" and like to keep up with the published litterature on wormholes and other "FTL" methods allowed by general relativity. However, I generally dislike arguments from authority, so I encourage you to attempt to follow the logic of the argument given below.)

First, I'll note that special relativity (SR) is a subset of general relativity (GR) - GR reduces to SR in the limit of flat spacetime. Thus, although GR is a theory of gravity, it also includes everything from SR.

Now GR draws on differential geometry, which is about describing curved hypersurfaces (or non-hyper 2-d surfaces, for that matter) without embedding them in a higher dimension. One tool for doing this is the coordinate patch. Imagine, for example, the world of one of those 80's computer games (like asteroids) with wrap-around screens. If you go off the right side of the screen, you re-appear at the left side at the same verticle coordinate. You could imagine having the same game displayed on two screens, but the second screen's display is displaced from the first screen's distplay by half a screen width. That is, the asteroid-blasting spaceship that is split between the left and right sides of the screen on screen one is in the middle of the screen on screen 2. Both screens are two ways of representing the same internal state (our analogy to physical reality). They involve two different ways of assigning coordinates and splitting them up to describe the same underlying thing.

Unlike Asteroids, however, in GR time is one coordinate which, like other coordinates, can vary based on how you observe it. Rather than having a geometry that describes space, you have a geometry that describes a unified space-time.

So lets look at the simplest wormhole - the Visser wormhole. Visser wormholes can take the form of many shapes, but let's take one that is a circle. Consider two regions of flat space-time, lets call them S1 and S2, separated by a very large distance. Except that in each region, we define a circle of equal diemsnions, and identify the coordinates on one side of the circle on S1 with the other side of the circle on S2. This is much like the wrap around screen example, where we identify the coordinates of one side of the screen with the other side. Much like the Asteroids game example, the physical reality that these coordinates represent have points adjacent to one face of the circle on S1 adjacent to points near a corresponding part of the face on S2. Also similar to the Asteroids game example, an entirely equivalent description of the physics would be to "cut" our coordinates not inside the circle, but in the plane of the circle outside the circle while keeping continuity of the coordinates through the circle's inside. This would have again two sets of space-time coordinates which we can call T1 and T2, where T1 is all points to the "left" of the circle (considering the circle to have left and right faces) in S1 and to the right of the circle in S2, while T2 is all points to the right of the circle in S1 and all points to the left of the circle in S2. In both descriptions (S and T) all points are represented, it is just that in S you make a jump from one patch to another when you go through the circle but not when you go around the circle, while in T you make your coordinate jump when you go around rather than through.

Now note that except at the circumference of the circle itself, space-time is everywhere flat. This means that special relativity applies everywhere, whether you go through the wormhole or around the wormhole.

Next, we will say that the regions of flat space-time, S1 and S2 (or equivalently T1 and T2) meet up into one continuous region of flat space-time if you just extend them far enough. Each loop of our Visser wormhole might be located far from its partner when you "go around" the circle though the S descriptions of the geometry. Also, because this is space-time rather than space, each end could be moving at a different velocity from within the same frame of reference.

"Stross had this idea in Accelerando where post-humans would create ghosts of themselves to do tasks in virtual space. It's not just a visual thing like Dr. Manhattan in Watchmen where all of his sub-parts were controlled by the same mind. It's more like "Someone just mentioned something I don't know. Sub-me, go study it in accelerated time and report back to me." Sub-me's knowledge reintegrates with the primary personality so that it can be recalled with the same ease of having spent the time studying it himself -- because he already did in a way. If these ghosts accrued sufficient experience, they might consider themselves their own sovereign intelligence and refuse reintegration. Whole cans of worms to be found here."

"A full clone of the mind might consider that subjective experience is the only way a mind is built and the merging of itself back into the parent mind is not death since those experiences will become a part of the mind and inform its actions."

Also keep in mind that AIs, and transhumans with artificially altered brains, might well perceive the question of self-identity very differently from we do. They mind feel comfortable and natural doing things that would make us queasy.

I think that the "reintegration isn't death since my memories remain" thing makes sense, provided the clones haven't diverged too much. However, what if the clones develop philosophical differences - say, one turns to the Dark Side while the other stays on the Light Side. Each would be horrified to receive the other's memories and personality elements, which would risk "poisoning" him and turning him away from his cause. Or maybe it's just that your other self has developed a hobby which you consider disgusting, and don't want to have retroactively experienced firsthand.

"The Orion's Arm philosophy of continuous death says that we're constantly changing states so we're constantly a different person from second to second, just that the changes are very minute on that scale."

Something I am well aware of (the idea, not Orion's Arm), and have considered in terms of its implications on immortality. Particularly, it's possible that at some point your future self's personality may change in a way that your past self would be horrified or just disappointed by. Your future self may stop caring about something that your past self was really excited about, etc. A formerly idealistic person might give up on his ideals after a traumatic experience, but his past self would feel betrayed by this, and would be angry with his future self for failing to uphold his ideals.

How can you guarantee immortality when you can't even trust yourself to stay you?

Or I could choose to trust myself, and assume that if at some point in the future I change my mind about something, then since it's me, I must have a good reason.

"That would be the obvious flaw in the plan. I have a feeling he might call it the Babel Project because religious groups would see his death-cheating as an affront to God and he would relish making it all the more overt."

He named it after a project that failed because the participants couldn't work together? What was he expecting?

Now suppose Andy is sitting next to the circle in S1. And we will suppose Andy's friend Bob is sitting next to the circle in S2. We will place both of them in T1 (we will let T2 be empty right now). Because space-time is both flat and continuous through the circle (as shown by the T1 description) Andy and Bob are at rest with respect to each other when considered through the circle. However, since the frame of reference S1 may be moving at high speeds with respect to the frame of reference S2 when viewed around the circle, And and Bob will not necessarily be at rest with respect to each other around the circle.

As you can see in the T1 description of the physics, if Andy has has two synchronized watches, and he hands one of those to Bob through the circle, then thenceforth Andy's watch and Bob's watch will continue to be synchronized when viewed through the circle. However, when we have Andy communicate with Bob over the light years that separate them along a path outside the circle, because they are moving at high relative speed with respect to each other they will see the usual special relativistic effects of time dilation occurring.

Now let's make things a little bit more concrete. We will have both circles initially start out close to each other - separated by 10 meters, say, and where passing through takes you to the same time coordinate. Andy stays with circle 1 in S1 and Bob stays with circle 2 in S2 as circle 2 and S2 are shot off at 0.995 times the speed of light (relative to S1). 0.995 c is a time dilation factor of 10. As Andy watches the circle recede through his telescope and computes its position in his reference frame based on observations around the circle, he will figure that it passes a point 9.95 light years away at a time (9.95/0.995)=10.00 years in the future. However, due to time dilation (or length contraction - they are two ways of looking at the same thing, what is time dilation in Andy's frame of reference is length contraction in Bob's), Bob will measure on his watch that one year will have passed as he passes that point which Andy thinks is 9.95 light years away (Bob will measure it as 0.995 light years distant, of course, due to length contraction).

As Bob recedes, Andy can look through the circle to see Bob floating just a few meters from him, with time passing at the same rate for both of them. As Bob passes that distant point 9.95 light years from Andy, when looking through the circle Andy will also only have had to wait 1 year for that event to occur even though he will have to wait 10 years (for Bob to get there) plus another 9.95 years (for the light to get back to him) when looking around the circle.

The whole causality violation thing happens when Bob stops at that point 9.95 light years from Andy, turns around, and comes back at 0.995 c. Using the same argument, when viewed from around the circle Andy measures it takes 20 years for Bob to get back. However, when viewed through the circle Andy measures it takes 2 years. So when Bob gets back he can step through the circle and see Andy two years after launch, or step around the circle and see Andy 20 years after launch. So now he can take messages from the later Andy back to the earlier Andy 18 years earlier.

(I'll not go into the various causality protection mechanisms that might be enforced by physics in this post - it is long enough).

"The other angle is that the backup is the person. Fire him up, let him live a little in virtual, then drop the bomb -- you are not you, you are the backup. We can give you a real body and let you loose in the real world if you do X for us. Do you trust them? Will you be willing to betray yourself?"

How strongly would you want to live in the real world? If your simulation is sufficiently cozy, and has a simulated universe-sized area to explore, then you might as well stay there. The one problem with this is that the real-world people controlling your simulation are essentially "gods" from your vantage point, and could quickly make your simulation very unpleasant if you displease them. The chief reason for wanting to exist in the real world would be to have power, not material comforts (which can be simulated just fine).

Correct as in 'established physics' or correct as in 'plausible and consistent with established physics?'

The second. Quantum fluctuations do build up to large amplitudes with one or two wormhole paths that make time machines, and it is thought (although not absolutely certain) that the amplitude will be large enough to either collapse one wormhole in the path or make them "bounce" away from their original paths to prevent the formation of a time machine. The general case has not yet been calculated. Hawking has hypothesized, however, that any time machine will be prevented by a similar mechanism. Whether the "Chronology Protection Postulate" is true remains to be proven (or disproven, as the case may be).

I think that the "reintegration isn't death since my memories remain" thing makes sense, provided the clones haven't diverged too much. However, what if the clones develop philosophical differences -

That was discussed in Orion's Arm where a giant war cut off sub-personalities from their originals. They basically had to become the originals.

If you think about it, corporations are basically the AI horror we've all been dreading. Ok, no, they're not running on intimidating servers with arcing lightning and flashing lights with hunter-killers hunting us down but they're inhuman, have inhuman goals and are essentially immortal barring accident or misadventure. I think someone else has already brought up that point.

So as an example of this, Fanta.

Fanta originated when ingredients for the production of Coca-Cola became difficult to obtain in the company's Germany plant during the build up to World War II.[2] As a result, Max Keith, the man in charge of Coca-Cola's operations in Germany during the Second World War, decided to create a new product for the German market, using only ingredients available in Germany at the time,[2] including whey and pomace – the "leftovers of leftovers", as Keith later recalled.[3] The name was the result of a brief brainstorming session, which started with Keith exhorting his team to "use their imagination" ("Fantasie" in German), to which one of his salesmen, Joe Knipp, immediately retorted "Fanta!".[3]

Even dicier was IBM's Third Reich ties. The little blue numbers tattooed on the arms of concentration camp prisoners were the primary key for an IBM database. IBM Germany serviced those machines during the war even though this subsidiary was cut off from the corporate parent. After the war, IBM was in the dubious position for suing for profits owed due to war-time work in those concentration camps. So when you mention turning to the Dark Side, boy howdie at that!!!!

say, one turns to the Dark Side while the other stays on the Light Side. Each would be horrified to receive the other's memories and personality elements, which would risk "poisoning" him and turning him away from his cause. Or maybe it's just that your other self has developed a hobby which you consider disgusting, and don't want to have retroactively experienced firsthand.

That happened in Accelerando where the ghost of a character had an affair with the ghost of another character. This was done as a REALLY elaborate handshaking process in accellerated time. The host refused to accept the reintegration of this ghost's experiences into his own mind because he felt it was the result of manipulation by his mother, trying to steer his development. Of course, the mother in question is not the one he grew up with -- she's dead. The mother in question now is the uploaded personality returned from an interstellar mission to explore the closest router of the alien wormhole network that is supposed to link all the stars together. The mother he grew up with kept experimenting to produce the ideal child and ran him through thousands of simulated childhoods experienced in realtime, hitting the reset button on every outcome she did not care for. She didn't realize he was journaling the entire time and so has the accumulated subjective experience of every one of those childhoods. GACK!

Luke said: I have a wormhole. Going from wormhole end A to wormhole end B takes me from a coordinate time of t to a coordinate time of t - 5 years.

There... Right there... That's where the confusion is. You send one end off at relativistic speeds but it still gets to its destination in the same time frame. It just gets there less older than the origin. A 1 light year trip at 0.8c still takes 1.25 years to get there, it just feels like 9 months. And once it is in place, the time dilation has no further effect.

Andy and Bob start at the same point (P0). Bob takes off at 0.8C towards his destination (P1) which is 1 light year away. In 1.25 years, Bob arrives at P1. Andy has experienced 1.25 years while Bob has only experienced 9 months.

Now assume that Bob's course was a light year circle. Bob doesn't arrive at 9 months, he arrives at 1.25 years having only experienced 9 months. There is no time travel, just time dilation.

About the only thing I understood clearly were the comments about Dune. Although they still invoke a form of magic through the use of "spice", the various effects such as plotting paths through space or predicting the future *could* be thought of as looking at the various world lines before quantum superposition collapses them into one. (I suppose you might say when various characters are examining the future, they are attempting to force a collapse on their terms).

Being somewhat old fashioned, I will stick with something that resembles the Alderson Drive, or cosmic (rather than artificial) wormholes. Cosmological features will (probably) not arrange itself to create closed timelike loops since that would be a more energy intensive feature, while non connected wormholes/tramlines would represent a least energy solution.

Andy and Bob start at the same point (P0). Bob takes off at 0.8C towards his destination (P1) which is 1 light year away. In 1.25 years, Bob arrives at P1. Andy has experienced 1.25 years while Bob has only experienced 9 months.

What you left out is that in 9 months, Andy has experienced Bob arriving at P1 when he looks through the wormhole. Looking around rather than through the wormhole, Andy still says that Bob arrives in 1.25 years (15 months).

So, from Andy's reference frame, 9 months after the wormhole launches, he can step through to P1. Assume the wormhole stops at P1, and define our coordinate system so that Andy is initially at spatial coordiante X=0 and time coordinate T=0. We have an event of launch at X=0, T=0. We have an event of Bob and Bob's wormhole arriving at P1 at coordinates X=+12 light months and T=+15 months in Andy's reference frame. And we have an event of Andy looking through the wormhole seeing Bob arrive at P1 while Andy is at X=0, T=9 months. At this point, the wormhole connects space-time coordinates X=0, T=9 months with X=12 light months, T=15 light months. That is, stepping through the wormhole takes you from X=0 to X=12 light months and T=9 months to T=15 months. Stepping back takes you from X=12 light months to X=0 and from T=15 months to T=9 months. The wormhole changes your spatial coordinate by plus or minus 12 light months and your time coordinate by plus or minus 6 months.

Now assume that Bob's course was a light year circle. Bob doesn't arrive at 9 months, he arrives at 1.25 years having only experienced 9 months. There is no time travel, just time dilation.

From his reference frame, Bob does arrive in 9 months. Through the wormhole, Andy sees Bob arriving in 9 months by Andy's clock, even though it takes 15 months for Andy to see Bob and Bob's end of the wormhole approaching Andy through flat space-time that doesn't go through the wormhole.

So we have an event of launch at X=0, T=0. An event of Bob and Bob's end of the wormhole arriving at X=0, T=15 months, and an event of Andy seeing Bob arriving through the wormhole at X=0, T=9 months. The wormhole now connects the last two events. When Andy sees Bob arrive through the wormhole, he can step through to just after the event where Bob arrives, going from time coordinate T=9 months to T=15 months, but now at X=0 in both cases. Similarly, Bob can step back from time coordinate T=15 months to T=9 months. The wormhole connects nearly the same spatial coordinate with a time coordinate changed by plus or minus six months. You now have a time machine were you can go six months back into the past or six months forward into the future.

This of course leads to paradoxical situations where you arrive at the wormhole, go back in time six months, wait for nearly six months and then shoot yourself before you have a chance to go through the wormhole. Did you or didn't you go through?

Strong telepaths could communicate / scan at longer range in hyperspace, and they were specifically developed by the Vorlons in the first place to act as weapons against Shadow vessels by "jamming" them. Also for exploring the whole "privacy" issue.

Not quite on the same scale as WH40K psykers, and I suppose they could have had "directed EMP weapons" or something to do the job, but as we're dealing with a big Lensman fan who's gone down the (IMHO rather silly) bio-ship route, why not?

I do wish they'd dumped all the prophecy stuff though :( .

David: "In all honesty, I'm just looking for an end result. I just need to cross the distance, and not have mad,insane, amounts of handwavium. I want room enough for a courier ship to jump from system to system, carrying essential messages like some futuristic Pony Express."

A special frame of reference (eg hyperspace) would be best I think. As above, you can say that "Einstein was bang on the money... except he never included hyperspace in GR theory".

Other than that, just describe it vaguely. Most readers won't want a David Weber-esque infodump every few pages: a paragraph or two to describe how the FTL drive works should be enough in most cases IMHO*.

* The exceptions being the really outlandish stuff or where it's absolutely central to the story, which doesn't sound like what you want.

After that, well you can tweak things as you want. Perhaps entering hyperspace gets easier for bigger / smaller masses or larger / smaller volumes. Perhaps a hyperdrive can be squeezed into a rucksack - or nothing smaller than a city block. Between the engineering & made-up physics you have available you should be able to come up with a reason why you get XYZ and not ABC.

jollyreaper: "But what is it about hand motions and spoken words that cause spells to work? What is it with symbols like crosses making vampires flee?"

You can always go the Discworld route - "things happen because people believe it" - although that means thoughts like "is everything real?" are... dangerous. That doesn't avoid the problem of describing faith or belief in terms of physics, but may offer an out.

Milo: "If you want to launch a ballistic missile, you're not going to rapidly type up a guidance system by hand before enemy forces overrun you. Instead, you are going to take a guidance system someone else programmed, and simply press a button."

I'm using something like this for the magic in a fantasy setting I'm also working on. Write down the (much longer) magic words etc, then have a verbal "button" that allows you to cast the rest. If you're really good, you can merely think the "button" (activation clause? Password? Whatever).

Geoffrey SH: "Jedi come to mind this late at night, but there are obviously others."

In personal combat and some espionage work, yes. They didn't do so well in other stuff. Heck, Geonosis in AotC was probably a serious defeat for the *Jedi*, given how many Jedi they lost in the battle in the arena, vs those 2-a-penny battle droids...

"40K does manage to tone this problem down somewhat- they are powerful, but often can be defeated."

But only by even more grimdark ;) .

jollyreaper: "The only kind I'll allow would be one based on seeing possible futures. It's a branching of possible actions based on the mind-state of living actors. So the future will be shifting from second to second as resolve waivers and new feelings come into play. You're seeing the echoes of potential futures."

I suppose if you have a good enough computer and can scan everything fast enough and with enough detail (without the observer effect...) then you could predict the future very accurately (how much do quantum effects make us change, say, our minds?). Until something un-scanned enters the picture at least or quantum mechanics pokes its nose in, in which case you'll have possible futures instead.

"Here's an idea cobbled together from a few different sources."

I admit to including telepathy in my setting, but only by making it more like a sort of combination of radio + telekinesis. That is, there's no reason why machines can't do it, and technically, there's no reason why it's just limited to communication. If telepathy can move the stuff in your brain cells so as to make you think something (eg hear the telepath's voice), it can also move stuff around inside a computer core with the same level of precision. That was the easiest way I had of making a scientifically plausible form of telepathy (no magic in my sci-fi setting).

Milo: "Something that stories about prophecies generally omit is how the existance of prophecies changes what will come to pass."

I'm using both divine and "self-made" magic (that is, magic you cast, not magic you ask a deity to cast for you), but there are what I think of as the "usual" restrictions - bigger is harder, precision is harder, etc. Groups of very powerful mages can call down a tornado, but you won't find some random schmuck doing it without divine intervention.

"If real life worked like that what you could do is take an orphan with cancer down to the track and tell his sister to bet her last dollar on the least likely horse so she can use the winnings to pay for his operation. There's no freakin' way that horse ain't coming in now. You make sure you put your own money down on it, too."

No. If real life worked that way, you'd be found out by some children & carted off to prison whilst yelling "It would've worked if not for those pesky kids!" :P .

"The caveat to "human nature never changes", of course, is that once you start heavily genetically tweaking the brain, you're not exactly human anymore. It's possible for transhumans to become very, very different. So it's an author fiat in this setting that they aren't."

We need a "GM Human" topic *cough*HinthintRick*cough*...

"So, tell me someone's already written this story. I'm sure they have and it was probably decades ago!"

No, but slight differences of experience once created would eventually cause the clones to diverge. Not much perhaps, but the potential's there.

"The rise of the simulationist trope brings that into question. If it's possible to fully model the planet within a computer system, why go to the bother of creating it in the real world?"

The Arisians liked to compare their "Visualisations of the Cosmic All" to reality (like comparing a computer model to reality), but other than that, they had no reason or desire (well, except "humanitarian" maybe) to interfere with others until the Eddorians came along and started messing around.

Milo: "Or would that clone go "Wow, I'm glad that the real Jollyreaper (who is not me) saw fit to ensure my creation! I like my newfound existance! Oh, and I seem to have his memories, too."."

It would come down to personal belief. Some people may just be too uncomfortable to go with downloading memories in the event of "body death" or whatever it's called. On the other hand, I can see being comfortable with it as a precondition of military service. There is of course a big difference between intellectually and emotionally coping with something like this. Maybe a use for those telepaths :P ...

"But how does magic respond to things being "done wrong"? Are there spirits who take offense at your actions, or does an impersonal force go "Bad command or filename."?"

Obviously the deity you request the help of is the ghost of Sir Humphrey Appleby.

Citizen Joe: "Now assume that Bob's course was a light year circle. Bob doesn't arrive at 9 months, he arrives at 1.25 years having only experienced 9 months. There is no time travel, just time dilation."

Correct, there is no time travel here. However, the time travel bit comes into play if you can make a wormhole between Andy & Bob. Stephen Baxter did it like so I believe (Luke please correct me if I'm wrong :P ):

T=0 @ Sol. Wormhole opens between starship + Sol system. Ship sets off at 0.9c relative to Sol on a huge round trip.T=0.0000001 @ ship. The voyage ends for the starship & people on the other end of the wormhole.T=1 @ Sol. Starship's voyage ends.

Thus, although T=0.0000001 time has passed for those manning the wormhole & ship, T=1 time has passed for Sol. The wormhole operators can now step through the wormhole and into the period T=1. Similarly, the ship's crew can step through to return to T=0.0000001 Sol. There is now a wormhole between T=0.0000001 Sol & T=1 Sol.

One thing to bear in mind with FTL of any kind (whether by wormhole, warp drive or hyperspace) is that it presupposes a very powerful use of gravity control. Once this Pandora's box is opened, we must assume that anti-gravity lifters, reactionless drives, inertial shielding, gravity lasers, gravity radio, etc. will have already been common place for at least a century or more.

The only way I can see around this is if there is a preexisting wormhole/stargate system conveniently left by an off-stage alien race, or possibly a natural "living" structure of the cosmos, like a galactic circulatory system. The wormholes might be just outside of the solar systems, necessitating some serious rocketry to get to and from, but still cutting travel times down to months instead of decades....

Correct, there is no time travel here. However, the time travel bit comes into play if you can make a wormhole between Andy & Bob. Stephen Baxter did it like so I believe (Luke please correct me if I'm wrong :P ):

I already did, see my reply to Citizen Joe.

Here' another attempt at explaining it. Andy and Bob are sitting in two chairs in the same room. Each of them wears a watch. There is no funny warped space-time or anything between them. I think we can all agree that Andy's watch and Bob's watch remain in sync. They both see time passing at the same rate, and see the other's time passing at the same rate they see their own time passing it. This is the normal, intuitive world we live in.

Oh, except I didn't tell you that the loop of a Visser wormhole surrounds the room. Andy and Bob don't know that, the wormhole loop is outside the room. As far as Andy and Bob are aware, the space between them is normal in every way (and it is, the Visser wormhole only affects space-time at its circumference, not in its interior). The plane of the wormhole bisects the room such that Andy is on one side and Bob is on the other. But we already know that Andy and Bob both agree that their timelines are advancing in sync with each other. If Bob measures it takes 9 months for something to happen within that room, Andy will also measure it takes 9 months. (presumably they are playing WOW or something to pass away all this time. I'll completely ignore details of how they hold their bladders for nine months).

Now Carl is outside the room, and sees the wormhole loop (for the sake of argument we will say that he is on the same side as Andy). Carl has a telescope. He sees the other end of the wormhole zipping away at 0.8 c. I think we can all agree that Carl's watch ticks along at the same rate as Andy's watch. But because Carl sees Bob's watch through his telescope receding at 0.8 c, he sees that Bob's watch is ticking only 3/5 as fast as his watch due to time dilation (as usual, this is after correcting for the time it takes for light to get from Bob to Carl). But since Carl and Andy are synchronized, and Andy and Bob are synchronized through the wormhole, then if Carl looked through the wormhole he would see Bob's watch in sync with his watch.

The wormhole completes its circular journey at 0.8 c. Time dilated Bob, looking out the window, sees that he arrives back where he started in 9 months. Andy agrees with Bob, he can get up from his chair, walk over to the window, see them arriving, and then go back to his chair. He can then open up his window and talk to Carl. But Carl, looking through his telescope, can tell Andy that Bob has not arrived yet, and will not arrive for another six months assuming that the wormhole stays on its current course.

Luke Said:Thus, although T=0.0000001 time has passed for those manning the wormhole & ship, T=1 time has passed for Sol. The wormhole operators can now step through the wormhole and into the period T=1. Similarly, the ship's crew can step through to return to T=0.0000001 Sol. There is now a wormhole between T=0.0000001 Sol & T=1 Sol.

The ship may have experienced 0.000001 units of time, but those units were dilated time units. Just because your watch is running slow doesn't mean that you're getting there any earlier.

Now, if the crew were watching the world go by, lets say on TV through the wormhole, everything would be in super fast forward. Meanwhile, ground control (watching the crew} would think that the crew was in suspended animation.

The crew might perceive it as time travel, but that is no more time travel than going into cryo sleep for a hundred years. It certainly doesn't go back in time or have causality problems.

"The only two reasons I can think of for that not to be the case: 1. There's some reason why they can't fully model everything in simulation space and need to do it for real in the real world. 2. Anti-simulationist bias which may amount to nothing more than personal aesthetic taste rather than for any practical reason."

#2 is a non-starter ass pull. #1 is a function of computational complexity, which gets really damn big for open-ended simulations - and depending on the detail required, quickly results in a computer bigger than the universe. Might as well use the universe itself.

Horselover Fat:

"And why does high stellar density make useful atmospheres less likely?"

More extinction-level radiation events means less life, and less life means lower probability of exygen atmospheres. Also, in particularly high stellar density regions, you have the potential for nearby supernovae which can disrupt atmosphere formation.

Rick:

"I gotta say that if you must have magic in a setting, I prefer it to be magical, not simply mechanistic with different laws."

What exactly do you mean by "magical" in this context, as opposed to "mechanistic"?

Milo:

"But how does magic respond to things being "done wrong"? Are there spirits who take offense at your actions, or does an impersonal force go "Bad command or filename."?"

More like the result of "rm -rf /" (which would be pretty much indistinguishable from a spirit taking offense, really).

Never heard of him. Some of the reviews are mixed. The kind of things I really hate are highlighted in one review.

There’s a political message here, too: megacorporations have financed most of the important scientific work involved in recreating Martian technology and rediscovering Martian space and history; an interstellar government called the Protectorate mostly exists to feed itself. There’s nothing new here: invasive but ineffectual government, and powerful but soulless corporations are another fixture of dystopian sci-fi.

Mostly, I feel like Morgan has a difficult time with Takeshi’s character. He’s a tough-as-nails mercenary, an ex-member of a much-feared (even mythologized) military group called the Envoys, but spends much of his time feeling traumatized, cynical, and disillusioned. As an allegory against economized warfare, it’s bald but convincing enough. However, Takeshi’s character development is so passive-aggressive that one could go crazy trying to empathize with him. He kills (not just bodily, but destroying “stacks”—the digitized consciousness—as well) without a twinge of conscience, but tends to fall in love easily, and is prone to fits of moodiness. By about halfway through the book, I was sick of Takeshi’s internal contradictions, and yearned for a character that at least knew what he stood for. Don’t get me wrong: I can appreciate moral grey area, but something about Takeshi’s moral ambiguity seemed insincere and irritating, for whatever reason, perhaps because his moral vacillation was entirely internal, while his external actions continued in the tradition of a bad action movie construct.

- Am I correct to think the virtual particle feedback loops will appear as soon as the spacelike separation between wormhole ends is insufficient to offset the timelike separation? (For example, when sending a wormhole away and then returning, shortly after the turnaround point?)

- Are there any wormhole geometries which allow for dilation effects through the wormhole which mimic the dilation experienced between the two surrounding spacetimes? (IOW, where the effects observed through the wormhole loosely match what some people intuitively think should happen?)

- Is the tunnel length between wormholes considered zero?

- Are there any effects on the wormhole itself from being accelerated to relativistic velocity (or is that something we won't know until a coherent theory of quantum gravity)?

"It is more complicated than that, since there is no way to determine simultineity. In other words, one observer might figure than in his reference frame you left Wolf 359 before you left Earth, and another would figure than in his reference frame you left Wolf 359 after you left earth, and both interpretations would be equally valid."

One has to make a distinction between observation and participation. Just because you observe photons from an even that happened closer to you before you observe photons from an event that happened further away, that doesn't mean the closer event happened first. For an example, an astronomer observes light from Vega a week before he observes light from Supernova 1987A. Does that mean the light from Vega was generate before light from the Supernova? No, obviously not. Vega is 25.3 light years away, and SN1987A is 168000 ly away. The light from the supernova was generated almost a 170k years ago. The light from Vega was generated in 1986.

But let's not get wrapped around the axle of what one can learn from observation. If any one actor doe things in temporal order, then causality will not be violated, even if light from his acts reach spme observer out of order. The actor still did his acts in correct order.

I rather like them. Morgan's pretty down on modern capitalism, so if that's a stumbling block, you won't like them much. As far as that particular review goes, it's half-right; most of the objections are a matter of taste. That being said, the reviewer in question either didn't notice or dismissed the explicit political framing of the main character, especially in the third book.

I think the mental powers of the Second Foundation are way more offensive than the Mule. The Mule, as a mutation, could possibly have the limited powers ascribed to him.

And I don't think Psychohistory was so much a handwave as a misunderestimation of how difficult it would be to quantify human behavior. It's improbable rather than implausible.

I never really cared about B5, so I have no opinion.

WRT Dune, it strikes me that Paul's power was not all that useful, even as prophecy. It turned out in the end that the future could be seen, but not changed. IOW, one can't say, "Repent or face the consequences." The only true statement about Paul's power would be: "If you don't repent, you'll get burned; If you do repent, something will go wrong anyway and you'll still get burned."

I don't have an opinion about the nature of the racial memory power. It came across in practice as a kind of psychological version of Lysenkoism. Bad science, but useful for storytelling.

BTW, throughout the Dune books actually written by Frank Herbert, reiligion was pretty clearly a tool of the powerful. The books were full of speculations about the nature and uses of religion, without any respect for the idea that they might be objectively true.

Anti-capitalism isn't my problem (copied an extra paragraph by mistake), it's piss-poor character development, the wall-banger stuff that makes you want to give up on reading. The description of the protagonist sounded like it could really grate on the nerves. I hate it when characters are written dumber than their backgrounds would indicate. A computer programmer suddenly on the run from shadowy government forces because he Knows Too Much(tm), I could expect a lot of panic and mistakes and possibly a few strokes of brilliant dumb luck not getting killed. But he's going to have to smarten up quick before the premise becomes ridiculous.

On the other hand, if the character is presented as an ex-military operator who's trying to live out a peaceful retirement when a local crime boss' goons Mess With The Wrong Guy(tm), I'm going to have certain expectations about the character. Cool demeanor, no bravado, competence at his craft, knowing how and when to pick his fights. The last thing I'd expect to see him do is strap on twenty guns under a trench coat, march into the boss' bar and go Matrix-style on everything.

Doing it right is drama; doing it wrong is melodrama. Two people could look at the same story and see it differently. I tend to read negative reviews first and see if my button-pushers are described. One of the biggest button-pushers for a series in general is "The author has no idea where it's going and isn't going to wrap it up well."

I'm just talking hypothetical characters here. I haven't read those books so have no opinion of how in or out of character Kovacs is. An artist who cares nothing of patriotism and martial glory finds himself drafted and serving on the front lines of a major war would naturally feel ambivalence about the whole military thing. A major general having ambivalence about the need to fight wouldn't make any sense unless it's because he's put in a situation of doing something he feels goes contrary to the oath he took, i.e. turn your guns on your fellow citizens. That's the personal crisis civil wars are made of.

One has to make a distinction between observation and participation. Just because you observe photons from an even that happened closer to you before you observe photons from an event that happened further away, that doesn't mean the closer event happened first.

My statement was not about the order of detecting photons. It was about the time-ordering of events in a given frame of reference. This is one of the more counter intuitive elements of special relativity.

Suppose Alex, Brian, and Chris are all in a line at rest with respect to each other, and located one light year apart in their frame of reference. We may set up the coordinate system such that Alex is at X=-1 light year, Brian is at X=0, and Chris is at X=+1 light year. Brian sees a flash of light from both Alex and Chris at the same time. So Brian knows that one year ago both Alex and Chris shone their lights at him simultaneously.

Now lets consider Dave and Earl. When Brian sees the light from Alex and Chris, Dave and Earl just happen to be where Brian is. However, Dave is moving at 0.8 c towards Alex and Earl is moving at 0.8 c towards Chris. Dave's frame of reference is every bit as good of a frame of reference as that of Brian. But in Dave's frame of reference distances are reletivistically length contracted by a factor of 0.6, Alex is coming toward him at 0.8 c, and Chris is receding away from him at 0.8 c. Dave also sees both flashes at the same time. He solves for the time coordinate at which they will have to be emitted. In Dave's frame of reference, where T is the time coordinate in Dave's coordinate frame (all distance units are in light years and time units are in years):Alex's position X_A = 0.6 - 0.8 TPosition of Alex's light pulse X_AL = - TNote that this matches the known case of T=0 where the light pulse reaches Dave and Alex is at the (length contracted) distance of 0.6 ly from Dave. Dave solves for the time when Alex emitted the light pulse (when X_A = X_AL) and finds Alex gave his signal at T_A = -3 years. Now he repeats the same calculation for ChrisChris's position X_C = -0.6 - 0.8 TPosition of Alex's light pulse X_AL = Tand solves that Chris emitted his signal at T_C = -0.33333 years. Since Alex emitted his signal three years ago, and Chris emitted his signal 1/3 of a year ago, Dave concludes that Alex emitted his signal before Chris.

Now do the same calculations for Earl. He finds that Alex emitted his signal 1/3 of a year ago, and Chris emitted his signal three years ago.

Note that in all three cases, the light signals from Alex and Chris were seen simultaneously. However, Brian concludes that the signals were emitted at the same time, Dave concludes that Alex emitted his signal first, and Earl concludes that Chris emitted his signal first. This illustrates that in relativity it is impossible to agree on the time ordering of events.

What all observers can agree on is whether one event could affect another event. If Alex sends Brian a message, no observer will ever conclude that Brian receives his message before Alex sends it. But if there is not time for light to pass between two events then those two events can have any time ordering depending on the relative motion of the observers.

"It's the name of a character from a world settled by Japanese using Eastern European labor. And?"

And there's a difference between an in-story justification and being justified in the mind of the reader. I grew up with the whole Japanese-is-cool-beyond-question trope. I also went to school with 10-20% (depending on the school) Japanese-Americans. On top of that, I had a Japanese-American girlfriend for a while. The actual behavior of Japanese-Americans, and their reaction to tropes about the Japanese, was very instructive. So, just my informed opinion:

Part-Japanese characters in SF are, for the most part, attrocious. They totally get wrong how Japanese and Western cultures mix. The fanboy mysticism about everything Japanese, when applied to such racial and cultural hybrids is beyond laughable.

Am I correct to think the virtual particle feedback loops will appear as soon as the spacelike separation between wormhole ends is insufficient to offset the timelike separation?

That sounds about right. The actual condition is that some path (such as one through the wormhole and through normal space) that closes on itself has a light-like interval (and perhaps even a time-like interval, although no one has looked at that yet because they've only looked at light speed particles). Without wormholes you can see that any closed path in space-time must have a space-like interval.

Are there any wormhole geometries which allow for dilation effects through the wormhole which mimic the dilation experienced between the two surrounding spacetimes?

There are wormhole geometries where the time dilation effects are different on the two sides. This could happen if, for example, one wormhole mouth was much more massive than the other, so that you get more gravitational time dilation around the more massive mouth than the less massive mouth. So far there is no way to get the time dilation to depend on the relative motion - if the time dilation did depend on the relative motion for wormholes connecting a space-like interval, it would violate the central assumption of relativity (that all inertial reference frames were equivalent).

Is the tunnel length between wormholes considered zero?

It is for the Visser wormhole. There are other wormholes that can have very long tunnels through them (such as with some choices of parameters for the Kuhfitig wormhole geometries).

Are there any effects on the wormhole itself from being accelerated to relativistic velocity

There can not be any effect on the wormhole if its ends are moving with a relativistic velocity with respect to each other but connect a space-like interval. This, again, is from the central assumption of relativity. Presumably, very strong accelerations could break a wormhole, just as they would break a physical object. However, there is nothing to prevent accelerating a wormhole mouth at lower accelerations that do not break it to high velocities with respect to its partner.

What's your take on Heim-Droscher?

I have not looked into it in detail. A cursory review of the data (meaning I skimmed the Wikipedia article :-P ) indicates current versions of the theory are falsified by the non-existence of a neutral electron. I have vague recollections of claims that this class of theories allows various nifty effects such as reactionless motion or faster than light travel. If the theory allows the former it must be an incorrect theory of nature by Noether's theorem. Otherwise, I will wait for the evidence before coming to a conclusion.

It wasn't written in the 80s (really the height of American Japanophilia), it wasn't written by an American (Morgan's British), it's set 700-800 years from now, and the most Japanese thing about the protagonist is a taste for Ramen.

You probably wouldn't like it much, but for different reasons than you're assuming just based off the name.

You know, the thing that bugs me about Dune is not the prophesies and precognition, which are treated as being about as useful as they are in real life (not very, but taken seriously by some powerful groups, and having some poetic truth in retrospect). Rather, I find the high-tech devices on display to be less believable than the mystical aspects. The personal force-fields in particular seem like extreme authorial pleading to have knife fights and swashbuckling in a futuristic setting. And after the first half of the book, the force shields are largely forgotten. If Herbert needed knife fighting to be central to the plot, as he apparently did, he could have just outlawed projectile weapons throughout the empire--it worked for computers, after all. The notions of "honor" among the Houses would have enforced this ban. Plus the fact that all the serious players have atomic weapons and likely other world-shattering devices to be used if one of the Houses decides to ignore the rules of the game (personal dueling, assassination, poisoning, blackmail and coup de tat are all acceptable). But this business of a totally impenetrable force field generated by a belt buckle, except it doesn't stop slow things... and lasers... except no one wants to use lasers because the force field makes the laser gun blow up...

Takeshi’s character development is so passive-aggressive that one could go crazy trying to empathize with him. He kills (not just bodily, but destroying “stacks”—the digitized consciousness—as well) without a twinge of conscience, but tends to fall in love easily, and is prone to fits of moodinessI dunno, sounds like a few grunts I know.

Luke, thanks for attempting to explain this, but I've still got a deer-in-the-headlights expression.

I believe I will leave the high-end fizzicks to the professionals, this has turned out to be way over my mental-simulation paygrade!

Maybe there's sufficient ambiguity in the books that one can read whatever one wants into Dune. Or maybe I am more familiar than some of you with some of Herbert's sources of inspiration. But it seems to me the implications were quite clear:a) The oracular vision enabled one to know not only the future but also what's happening far away at the present. We also know from relativity (referenced in the books) that FTL could enable one to see the past or the future. I would therefore say that oracular vision was essentially FTL vision.b) c) The oracular vision was not pointless because causality does not flow from the past to the future. That was the whole point! The past and the future are one and the future changes its past through its vision. That or you have to conclude that the vision changed the future because, one way or the other, the visions clearly had effects, as in Oedipus. It was not a tool that could be used by any individual for her own purposes however.d) So there was "something to it". The phrase "higher order" was sometimes used, with reference to natural and supernatural alike which is not surprising because the supernatural was usually presented as being of this world even though religion spoke of another world. There was not one god but several. Their future (potential) existence created the conditions for their becoming. More importantly perhaps, there were historical forces at play. They were sometimes talked about in mystical terms and sometimes in racial terms. If you take that metaphor litterally, genes had another creepy role besides the bizarre "genetic memory" (which was not constrained to one's actual ancestors and wasn't really memory either by the way and was similar in some ways to oracular vision). These forces and the visions had long constrained people's behaviour like they would constrain the books' protagonists. So you could say they influenced religions indirectly. It was explicitely stated that the witches seemed to have been used.

"Andy and Bob start at the same point (P0). Bob takes off at 0.8C towards his destination (P1) which is 1 light year away. In 1.25 years, Bob arrives at P1. Andy has experienced 1.25 years while Bob has only experienced 9 months.

Now assume that Bob's course was a light year circle. Bob doesn't arrive at 9 months, he arrives at 1.25 years having only experienced 9 months. There is no time travel, just time dilation."

Yes. Now suppose Bob carried a wormhole with him, while Andy kept the other end. When Bob arrives - 9 months after the creation of the wormhole from Bob's frame - he checks up on lottery numbers and sends them through the other side of the wormhole, where the information is received 9 months after the creation of the wormhole from Andy's frame. Now Andy has lottery numbers from 6 months in the future.

Tony:

"IOW, one can't say, "Repent or face the consequences." The only true statement about Paul's power would be: "If you don't repent, you'll get burned; If you do repent, something will go wrong anyway and you'll still get burned.""

I think true prophecy would be more along the lines of, "I predicted that you will repent and therefore not get burned, as long as I issue you this warning.".

Criminy jeez, what have I let loose here? I expect the GR discussion to be a head exploder, but so is the other subthread.

On the constraints of prophesy, shamelessly pimping an old post. (And also my historical fantasy novel, Catherine of Lyonesse, which stubbornly clings to life in the marketplace.

What exactly do you mean by "magical" in this context, as opposed to "mechanistic"?

It was a lot easier for me to write the line referred to, than to fully explain it. It is more a matter of flavor, perhaps, than of formal structure, but I'll link to an even older post, from the early days of this blog, that says something more about it. (The three posts that follow it continue the discussion, more or less.)

You guys keep ignoring my statement that time dilated time is DILATED. Yes, Bob is only 9 months older, but they are 9 dilated months. Andy is 15 months older but his months aren't dilated. In this case, Bob's dilated month takes 50 days (in Andy's time frame). If Bob and Andy are computers, then basically Bob's clock speed got slowed way down.

That is also part of the big problem with relativistic travel, particularly up around 0.9c. Not only do you have a ridiculous amount of kinetic energy, but the time to threat is reduced greatly, and your reaction time is totally shot (like a hundred rest frame hours go by in the blink of an eye).

Agreed. Dune is one of the few SF universes (that I can think of) that convincingly deals with the time-traveling implications of FTL by making it integral to the plot. The Guild Navigators are able to receive information from numerous possible futures, it would seem. It may be that when traveling by FTL, choosing a paradox-inducing route leads to destruction of the ship, or possibly being "edited out" of the common timeline?

As far as literature goes, prophesies of the future being integral to the plot are a common enough trope. Of course, these prophesies rarely come to pass the way the characters assume they will, often with an ironic twist (Macbeth being a prime example). And in real life, there are plenty of (too many) people that take their favorite prophesies of doom WAY too seriously. But that's a discussion for another thread...

The issue for an SF world-builder trying to hew to hard science is that FTL is either a) impossible because it violates causality, or b) possible because causality doesn't work the way we think it does (in a linear fashion). So if you want FTL in your universe, you've got to either ignore this fact (use handwavium) or deal with it in some sort of internally consistent manner.

While most space opera chooses the former, Dune goes with the latter, giving all the major factions an expanded sense of time and key information from the future(s). This is one of the reasons why Dune holds up so well in the 21st century.

As for the retro-action in a futuristic setting, this has been going on since at least the 30's. (Flash Gordon and John Carter used swords when ray guns or firearms were certainly available.) Herbert's particular explanation for why this would be the case comes off as a bit too overwrought, considering that computers and robots are not in use for purely cultural/legal reasons. The only really plot-pivotal knife fight is at the climax, between Paul and Feyd. Why doesn't someone just shoot Feyd? Because it would be dishonorable (he invokes the rules of kanly, after all) and make Paul's ascendance to the throne less legitimate than it already is. Neither one of them is wearing those force-field belt buckles at the time, anyway...

As for the retro-action in a futuristic setting, this has been going on since at least the 30's. (Flash Gordon and John Carter used swords when ray guns or firearms were certainly available.) Herbert's particular explanation for why this would be the case comes off as a bit too overwrought, considering that computers and robots are not in use for purely cultural/legal reasons. The only really plot-pivotal knife fight is at the climax, between Paul and Feyd. Why doesn't someone just shoot Feyd? Because it would be dishonorable (he invokes the rules of kanly, after all) and make Paul's ascendance to the throne less legitimate than it already is. Neither one of them is wearing those force-field belt buckles at the time, anyway...

I can see swordfights preserved as ritual combat for the social elites if there's a huge cultural brain bug about honor being a matter of life and death. I could see it as a case where the young men and women of noble families have to train to fight and their elders wax philosophical about how the shedding of blood keeps up the robust vibrancy of their culture. Social critics would content that it's backwards, barbaric, and stupid but have little impact.

What I have a really hard time rationalizing is the use of bladed weapons alongside firearms in serious warfare, no rules all-out combat. You could MAAAYBE try to rationalize that blaster pistols have a long recharge time and so you fight with a lasersword in one hand and a blaster in the other. But gee, wouldn't someone think to reinvent a revolver?

About the only way to rationalize a lightsaber would be precognitive powers like the Jedi and it would STILL make more sense for them to fight with blasters. You can only hit someone within a few meters of you with the lightsaber but you can shoot someone a kilometer or two away due to your force-assisted aim.

The kind of awkward, painful kloodge you'd need to justify rapid-fire automatic weapons and hand weapons in a fight is saying that the armor is so freakin' awesome that it'll turn most laser and projectile fire but would be vulnerable to melee attack, either crushing through a hammer impact or a thin blade pushing through the joints. That's a huge pile of kloodge right there.

As much as I love Star Wars (the originals, at least) it is about as soft as science fiction gets. But if we want to start applying rigorous logic to a space-fantasy, I guess you can argue that the lightsaber is a defensive weapon, meant to protect one from blaster fire, killing and dismembering only when absolutely necessary.

But, yes, I agree that mixing swords with projectile weapons in an all out combat situation is ridiculous in the extreme. I wouldn't mind seeing a far future scenario in which all weapons are outlawed, except for the hell-class mega-weapons used by the military, pirates and terrorists. Personal combat is limited to empty-handed martial arts and improvised weapons, and is extremely rare. The population(s) are mostly either bio-engineered or medicated for passivity and non-violence, with those even capable of violence relegated to the police, military or outlaw status. Even the police are limited to non-lethal weapons. Any organized use of lethal tactics or devices will be quickly dealt with by the military, space patrol, etc.

There's got to be a good book or two that have used such a scenario. Larry Niven's Known Space comes to mind, before they encountered the Kzin, at least. Can anyone suggest some others?

I thought the point of the shields was to give different combat shields to the desert tribes. And to keep everything as medieval as possible of course. Ibn Khaldun doesn't work so well in the industrial age. Poor believability, I agree.

But there was worse if you care to think about it as usual. Like why go to such extents to conserve and collect water when the planet's poles will do it for you?

Been there, done that. Apparently a wormhole, including its mouths, can only exist in one frame of reference at a time. Just because physicists like Susskind and Hawking agree on and write about the clock-slowing nature of time dialtion, it apparently doesn't matter when people want to inisist that relativistic wormholes imply time travel. After all, we have the testimony of SF-writer physicists like Baxter, who use wormhole time travel as foundations of their future histories.*

*We'll just ignore that Baxter also wrote about high energy life forms existing in the first seconds after the Big Bang, but who were made extinct by the cooling of the universe. Or that he once invoked a man who was not born, but existed in a time travel loop so he could be present for a single event in the history of the universe. After all, it's his speculation about wormhole time travel that we want to say is hard science.

Paul's vision led him to try to change the future, but he couldn't. Likewise, Leto II felt trapped by his prescience, not empowered by it. Rationalizing about the nature of the vision is pointless. From internal evidence, visions of the future told you what was bound to happen, not what one could avoid by doing something different.

Speaking of which, I never detected any FTL connection to the visions of Paul or Leto II. Apparently only the Guild navigators could make affirmative choices based on their visions.

"I thought the point of the shields was to give different combat [skills] to the desert tribes."

The point of the shields was to create an environment in which individuals could plausibly engage in combat. Can't have a very interesting story if a breakdown in civility means shotguns-across-the-dinner-table. Swordplay is much less messy and a lot more personal.

"But there was worse if you care to think about it as usual. Like why go to such extents to conserve and collect water when the planet's poles will do it for you?"

Because the problem was the total quantity of water available, leading to very dry tropics and subtropics. The point of Kynes's program was to humidify the dry parts of the planet. Of course, he apparently didn't get the sandworm's part in the water cycle of Arrakis...

You guys keep ignoring my statement that time dilated time is DILATED. Yes, Bob is only 9 months older, but they are 9 dilated months. Andy is 15 months older but his months aren't dilated. In this case, Bob's dilated month takes 50 days (in Andy's time frame). If Bob and Andy are computers, then basically Bob's clock speed got slowed way down.

How is that possible? Bob and Andy are at rest with respect to each other (AT REST - see, I can use capitals, too). If you are at rest with respect to someone, neither of you experiences any time dilation with respect to each other.

(Now, it does get a bit confusing because Andy and Bob are also IN MOTION with respect to each other while simultaneously being AT REST with respect to each other.)

Or consider Alice and Betty. Alice and Betty are moving with a relative speed of 0.8 c (with no wormholes). Alice looks at Betty and after taking measurements, accounting for light time of flight, and so on, concludes that Betty's clock is only going 60% as fast as hers. Betty, of course, sees no such thing. As far as she is concerned, she is at rest and it is Alice who is moving at high speed. Further, when Betty takes measurements, she comes to the conclusion that it is Alice's clock that is slowed down to 60% of the correct speed.

So who is being DILATED? Alice or Betty?

Or perhaps this analogy will help. The mathematics of changing speeds in special relativity is the same math as rotations in Euclidean space. (It is a rotation through an imaginary angle, but that's minor). So consider Claire and Dana. Clair and Dana are enjoying a Saturday out in Seattle (it is August, about the only time of the year when Seattle is likely to be sunny, and these two friends don't want to miss the opportunity). They visited the Pacific Science Center, and are now outside in Seattle Center looking at the Space Needle. Claire sees that the space needle is 100 meters ahead of her. Dana is standing at a 45 degree angle with respect to Claire, but otherwise right next to Claire, and so she sees that the Space Needle is 70 meters in front of her and 70 meters to her right. From Claire's point of view, Dana's measurements are front contracted, everything is only 70% of the distance in front of Dana as it is in front of Claire. Does this mean that Dana is somehow squished front to back?

Remember, any time being measured by someone who is not right there is a coordinate. Does that fact that from Alice's point of view some of Betty's time coordinate is rotated into some of her distance coordinate change what is physically happening?

Okay, I'll answer that. No. Coordinates have no physical meaning. They are a convenient way that allows us to organize the relation between events. It is events and their intervals that have physical meaning. So if Alice (or Andy) sees Betty's (or Bob's) time being dilated according to her (his) coordinate frame, that is not an indication that there is a physical dilation going on at Betty (or Bob).

Not really. Their functions are powered by user bodily movements, and the user has to eat and consume a certain amount of supplemental water. So, while very efficient, they aren't 100% efficient, which pute them in the realm of improbability, not impossibility or even implausibility.

The books have many visions about the future which never come to pass. That will be very, very obvious to anyone who reads them.The navigators are the ones portrayed as being the ones most ineffectual when it comes to preventing their visions from coming to pass (they were destined to lose).I will not answer you further on this matter.

Been there, done that. Apparently a wormhole, including its mouths, can only exist in one frame of reference at a time. Just because physicists like Susskind and Hawking agree on and write about the clock-slowing nature of time dialtion, it apparently doesn't matter when people want to inisist that relativistic wormholes imply time travel. After all, we have the testimony of SF-writer physicists like Baxter, who use wormhole time travel as foundations of their future histories.

Baxter is unimportant. If you want the testimony of physicists who work on wormholes, I direct you to

And since you want to bring up Hawking, I'll point out that he is fully aware of the possibility of wormholes forming time machines, agrees that by general relativity they will form time machines, and has considered the issue in detail (including looking at reasons why time machines might be prevented, which is not because everyone agrees that Bob is time dilated). See

It's a neat philosophical question, but it's only relevant WRT to Alice and Betty taken in isolation. Every possible observer of the exercise is moving at close to the same relative velocity as either Alice or Betty. Either the entire universe is traveling at .8c, and one person is sitting still, or everone is traveling at a collection of relative velocities within a few hundred kps of each other, and one person is traveling at .8c. Which may also be a philosophical question in the physics classroom, but probably has a real world solution.

Perhaps we should make clear here that the relativity we are talking about -- relative motion -- is special realtivity. General realtivity is a theory of gravity. Why are you presenting general relativity arguments?

"Perhaps we should make clear here that the relativity we are talking about -- relative motion -- is special realtivity. General realtivity is a theory of gravity. Why are you presenting general relativity arguments?"

Perhaps we should make clear here (for the nth time) that special relativity is a special flat-spacetime case of general relativity, which is more than just a theory of gravity (and also the theory which allows for wormholes in the first place). Why are you so aggressively misunderstanding the theory?

I'm actually wondering whether the theory is meaningful in the real world, WRT time travel predictions. If the theory is correct, I'm not convinced that wormholes would be traversible, if they have had their mouths separated at relativistic velocities. Or, if wormholes that have been separated at relativistic velocities are traversible, I'm skeptical of time travel, because I am convinced of conservation of chronology.

Perhaps we should make clear here that the relativity we are talking about -- relative motion -- is special realtivity. General realtivity is a theory of gravity. Why are you presenting general relativity arguments?

For the issue of wormholes and time machines (which is what we are discussing, as far as I am aware), we need a geometric description of spacetime. Space-time cannot be everywhere flat (otherwise you wouldn't have a wormhole), and thus we need what is ultimately a general relativistic treatment.

However, please note that Raymond is right - special relativity is a subset of general relativity - the case where spacetime is flat. Whenever speacetime is flat, general relativity reduces to special relativity. General relativity is perfectly capable of dealing with relative motion, and will do so whether or not spacetime is flat.

I have been trying to use an example that invokes general relativity as little as possible. In the Visser wormhole, spacetime is flat everywhere except for certain singular points. Thus we can use special relativity to evaluate the intervals and relations between events and observers connected across those regions of flat spacetime.

As opposed to what, exactly? The fair and just society we have presently? I'm not even saying I'm in favor of such a completely unarmed society, but it's well within the realm of possibility. And it's a more believable form of authorial fiat if you want to settle dramatic conflicts with personal combat, rather than giving everyone magic force fields that only allow slow things to enter...

Not really. Their functions are powered by user bodily movements, and the user has to eat and consume a certain amount of supplemental water. So, while very efficient, they aren't 100% efficient, which pute them in the realm of improbability, not impossibility or even implausibility.

The sticking point I thought was evaporative cooling. You sweat, it evaporates, you cool down. If the sweat is never allowed to evaporate but is contained within the suit then you never really get to cool off, right?

Ok, looked it up. According to wiki...

In his essay "Stillsuit" in The Science of Dune, John C. Smith suggests that "Stillsuits designed using strict literal interpretations from the Dune books probably would not work and most likely would cook the wearer like a Crock-Pot ... However, engineering solutions can be envisioned for all the suit's shortcomings."[3]

The subsequent links are dead so I can't find the suggested solutions.

So I'll upgrade the stillsuit from "impossible" to "more than likely impossible."

"As opposed to what, exactly? The fair and just society we have presently? I'm not even saying I'm in favor of such a completely unarmed society, but it's well within the realm of possibility. And it's a more believable form of authorial fiat if you want to settle dramatic conflicts with personal combat, rather than giving everyone magic force fields that only allow slow things to enter..."

The problem with authorial fiats that depart from what we know about human nature is that they leave too many loose ends. So you have a society in which only the authorities and criminals even have a motivations to settle things with force, because everybody else is too drugged or genetically indisposed to care. Why would the said authorities and criminals limit themselves to only hand-to-hand combat? If they're the people with free will, it makes no sense whatsoever. Eventually an escalation spiral would ensue, probably something similar to the one that led youth gangs from switchblades and bicycle chains to pistols and AK-47s.

And the shields in Dune weren't magical. Because molecules in the air zip around at considerable velocities, someone using a shield was trapped in a bubble of progressively more and more stale air, which he could only escape by winning a fight quickly, by turning the shiled off, or by retreating. The shield-induced deprecation of energy weapons is a bit tougher to swallow, but for reasons of strategy, not magic.

I'm actually wondering whether the theory is meaningful in the real world, WRT time travel predictions. If the theory is correct, I'm not convinced that wormholes would be traversible, if they have had their mouths separated at relativistic velocities. Or, if wormholes that have been separated at relativistic velocities are traversible, I'm skeptical of time travel, because I am convinced of conservation of chronology.

You are right to be skeptical of interpretations that violate causality. Many of today's brightest physicists have likewise been skeptical. However, solutions to the causality problem, if they exist, occur outside of the realm of general relativity. The best candidates take place in quantum field theory, which allow the relatively benign levels of time travel which do not have closed time-like loops (and thus preserve causality), but alter any configuration of space-time that is about to form a closed light-like or time-like loop (and thus form a time machine).

So, here's the state of current understanding of wormholes with regards to time machines:

[1] Wormholes are a valid geometry in general relativity. They require rather odd conditions to be stable (regions of space-time with negative energy density in some reference frames), but these conditions have been observed in real life and are a matter of magnitude rather than of kind.

[2] Wormholes connecting two places (and times) in the same universe might be forbidden by physics. It is not clear if physics allows the topology of space-time to change and a wormhole to another point in the same universe has a different topology than the same universe without a wormhole. If the universe starts off with a simply connected topology and topology cannot change, you can never get wormholes within the universe. (You can still get wormholes between universes, and if topology cannot change such a wormhole could never be entirely collapsed - there will always be that connection between the two universes. However, two universes connected by a single wormhole never have any issues with causality violation.)

[3] Wormholes connect one region of space and time with another region of space and time. The relative motion of the ends can change both the amount of space and the amount of time that changes when you go between the ends. This opens the possibility of a wormhole or network of wormholes allowing paths through space-time that meet themselves (that is, they form a time machine).

[4] A wormhole that is about to form a closed light-like loop (that is, which is on the verge of becoming a time machine) will form a perfect resonator for quantum fluctuations propagating at the speed of light, going around the closed light-like loop, meeting up with themselves, and amplifying themselves to high amplitudes. It is highly likely that the amplitudes will be so large that any configuration of one or two wormholes that is about to become a time machine will experience such high amplitudes of these fluctuations that either one wormhole in the network will collapse, the wormhole ends will experience a strong force that "bounces" them away from a configuration which allows a time machine to form, or other alterations will be made in the geometry of space-time to prevent a time machine - although without a fully quantum theory of gravity we remain unsure of the effects these fluctuations will have on wormholes. No one has yet (that I am aware) worked out what will happen for paths that go through more than two wormholes although it is strongly suspected that the same effects will occur. Many (such as Hawking) either suspect or believe that the same mechanism will prohibit any method of FTL from ever forming a time machine.

Hmmm, post didn't show up. In the off chance that it got lost rather than delayed, here it is again

Tony

I'm actually wondering whether the theory is meaningful in the real world, WRT time travel predictions. If the theory is correct, I'm not convinced that wormholes would be traversible, if they have had their mouths separated at relativistic velocities. Or, if wormholes that have been separated at relativistic velocities are traversible, I'm skeptical of time travel, because I am convinced of conservation of chronology.

You are right to be skeptical of interpretations that violate causality. Many of today's brightest physicists have likewise been skeptical. However, solutions to the causality problem, if they exist, occur outside of the realm of general relativity. The best candidates take place in quantum field theory, which allow the relatively benign levels of time travel which do not have closed time-like loops (and thus preserve causality), but alter any configuration of space-time that is about to form a closed light-like or time-like loop (and thus form a time machine).

So, here's the state of current understanding of wormholes with regards to time machines:

[1] Wormholes are a valid geometry in general relativity. They require rather odd conditions to be stable (regions of space-time with negative energy density in some reference frames), but these conditions have been observed in real life and are a matter of magnitude rather than of kind.

[2] Wormholes connecting two places (and times) in the same universe might be forbidden by physics. It is not clear if physics allows the topology of space-time to change and a wormhole to another point in the same universe has a different topology than the same universe without a wormhole. If the universe starts off with a simply connected topology and topology cannot change, you can never get wormholes within the universe. (You can still get wormholes between universes, and if topology cannot change such a wormhole could never be entirely collapsed - there will always be that connection between the two universes. However, two universes connected by a single wormhole never have any issues with causality violation.)

[3] Wormholes connect one region of space and time with another region of space and time. The relative motion of the ends can change both the amount of space and the amount of time that changes when you go between the ends. This opens the possibility of a wormhole or network of wormholes allowing paths through space-time that meet themselves (that is, they form a time machine).

[4] A wormhole that is about to form a closed light-like loop (that is, which is on the verge of becoming a time machine) will form a perfect resonator for quantum fluctuations propagating at the speed of light, going around the closed light-like loop, meeting up with themselves, and amplifying themselves to high amplitudes. It is highly likely that the amplitudes will be so large that any configuration of one or two wormholes that is about to become a time machine will experience such high amplitudes of these fluctuations that either one wormhole in the network will collapse, the wormhole ends will experience a strong force that "bounces" them away from a configuration which allows a time machine to form, or other alterations will be made in the geometry of space-time to prevent a time machine - although without a fully quantum theory of gravity we remain unsure of the effects these fluctuations will have on wormholes. No one has yet (that I am aware) worked out what will happen for paths that go through more than two wormholes although it is strongly suspected that the same effects will occur. Many (such as Hawking) either suspect or believe that the same mechanism will prohibit any method of FTL from ever forming a time machine.

Tony: I guess I should use the term "magic" in quotes. In other words, not based on any physical principle in which we are currently aware. Maybe "Clarktech" is the better word here.

But that's not even the problem with the force shields in Dune. The problem is that we spend a good deal of time setting up this device and all of its rules, and then it's never seen again in the second half of the book. So why did Herbert bother in the first place? The prescience and prophesy, on the other hand, are significant throughout and woven into the plot.

As for the unarmed society, it would have to be one in which surveillance devices were ubiquitous (as far-fetched as that may sound) and personal weapons simply aren't available. This is not so likely on a future earth, but more plausible on a closed structure like a station or domed colony or ship... you know, like where most SF stories take place...

"But that's not even the problem with the force shields in Dune. The problem is that we spend a good deal of time setting up this device and all of its rules, and then it's never seen again in the second half of the book. So why did Herbert bother in the first place?"

Herbert had to justify a society in which swordplay was possible. But once you get on Arrakis, shields go out the window, because they aggravate the worms. But swords are still en vogue, because you don't build special armies and weapon systems for a single planet. Okay, so it's a stretch. But it's not so much of one that the reader throws the book down in disgust.

"As for the unarmed society, it would have to be one in which surveillance devices were ubiquitous (as far-fetched as that may sound) and personal weapons simply aren't available. This is not so likely on a future earth, but more plausible on a closed structure like a station or domed colony or ship... you know, like where most SF stories take place..."

More likely the people who wanted to use force would adopt adaptations like frangible bullets that poke holes in people, but not in hulls.

I need to save Luke's wormhole examples to read and digest them at leisure. Because I can't pretend that merely skimming them makes me even kinda sorta understand this stuff.

A useful question - which I am in no position either to answer myself or ask Luke to answer for us - is what constraints, in story terms, need to be put on FTL to avoid violations of causality and/or GR.

I emphasize 'in story terms' because as writers we can get away without explaining how our FTL works, but we want to avoid travel routings and such that 'should' permit time travel if they existed.

On social violence, it isn't hard for me to imagine societies where it is quite rare, without these societies falling victim to armed bullies. This roughly describes many contemporary Western societies that lack the 'Murrican wild west mythos, etc.

And for that matter I'd guess that huge numbers of 'Murricans have never heard a shot fired in anger, even in parts of the country where people make a big deal of the 2nd Amendment.

But that doesn't help you at all in getting to high tech societies with swordfighting, which after all is plenty violent.

First, even strictly under special relativity, one's traditional notions of chronological order go out the window. As Luke detailed, there are scenarios using relativistic velocities which result in the order of events being different for different observers - even after lightspeed delays in observation are taken into effect. In the absence of a privileged frame of reference (something forbidden under both special and general relativity) there is simply no such thing as a definitive sequence of events. It's not even a numbers game, where the reference frame largely shared by most matter in the universe is given priority. All frames are equally valid, and by corollary, no one sequence of events is the "correct" one for the purposes of causality.

Second, wormholes under GR do allow for certain forms of time travel which don't form closed timelike curves. Bringing a wormhole out to Wolf 359 at relativistic speed sufficient to have a one year subjective travel time in the far end's frame will result in travelers from Sol moving forward in time approximately eight years (from Sol's reference frame) when they traverse the wormhole. It's a little counterintuitive, perhaps, but as long as the lightlike separation is greater than the timelike separation (and correct me if I flipped the signs on that one, Luke) there's no breach of causality.

Third, there are already some effects at the quantum level which are atemporal - most notably entanglement. Particles interfere with themselves all the time, so interference due to time travel doesn't violate causality in the same way it would in the macroscopic world. How a quantum-theory-based chronological protection effect would manifest is an open question, and depends on your interpretation of quantum mechanics. If such an effect exists, of course.

"A useful question - which I am in no position either to answer myself or ask Luke to answer for us - is what constraints, in story terms, need to be put on FTL to avoid violations of causality and/or GR."

- Special inertial frame of reference for FTL, which would produce effects similar to those described by Tony and Citizen Joe. Wormhole ends at relativistic speeds would have additional dilation effects not currently predicted by GR. The wormhole end being dragged to Wolf 359 would experience the same time dilation through the wormhole as around it. An observer on Earth would see the same trip time (just over 9 years) through the wormhole as it would through the surrounding spacetime. This, of course, would violate GR (or at least require an extension to deal with it).

- Assume the chronological protection conjecture is correct, and any wormhole on the verge of becoming a closed lightlike curve experiences destructive quantum fluctuations. This limits the network to a directed acyclic graph (I believe) and requires some math on the part of the author, but also results in an interesting terrain in both space and time which can be cleverly exploited.

This is Luke. Google is acting up, so I am posting this as Anonymous rather than from my account.

Rick,

A useful question - which I am in no position either to answer myself or ask Luke to answer for us - is what constraints, in story terms, need to be put on FTL to avoid violations of causality and/or GR.

Several possibilities come to mind.

[1] A special frame. From a given frame of reference, there is no ambiguity in time ordering. If all FTL takes place with respect to this frame, you don't have to worry about meeting your past self.

[2] Ancient relics. People cannot make their own FTL tramways, or jump willy-nilly as their whim takes them, but are rather restricted to following pre-existing FTL paths left behind by ancient super-beings, or which are relics of creation, or some such. Needless to say, these pre-existing paths do not connect space-time in such a way as to allow time travel.

[3] Chronology protection. If you try to make an FTL trip in such a way as to cause time travel, you get the build-up of quantum fluctuations which makes your trip impossible (perhaps in a method that involves your destruction). For example, if you try to jump from Earth to Tau Ceti, and shortly after you arrive someone else tries to jump from Tau Ceti beck to Earth last Tuesday, you get quantum fluctuations which either prevent the FTL gizmo from engaging, or breaking the weaker of the two FTL gizmos (while possibly damaging the other one, and/or wrecking the attached spacecraft, up to whatever level of collateral damage the author thinks is interesting). This would lead to traffic regulations enforcing a common frame of reference for FTL jumping on common FTL routes (backed up by the fact that anyone who tried to get around these regulations would be the weakest link in the time-travel chain - the link that would break because otherwise all the other people who are traveling legally would need to break). When exploring new worlds beyond the usual traffic network, the explorers are free to set up the jumps as they desire since there will not be other connections that will interfere with them.

"On social violence, it isn't hard for me to imagine societies where it is quite rare, without these societies falling victim to armed bullies. This roughly describes many contemporary Western societies that lack the 'Murrican wild west mythos, etc.

And for that matter I'd guess that huge numbers of 'Murricans have never heard a shot fired in anger, even in parts of the country where people make a big deal of the 2nd Amendment."

The violence isn't there, but only through mutual agreement that sufficient justice is being done (and sufficient crime can proceed) without violence. Change people's perceptions about those things, and a significant number of people would cowboy-up. For example, in a resource crisis, people can get to be quite nasty towards each other, regardless of their previous behaviors.

WRT American conditions, I can only observe that the level of official reverence for the Second Amendment has little to do with the absolute number of guns in society, but it does have quite a bit to do with their relative distribution between criminals and law-abiding citizens. Of course, that's almost by definition, because when guns are illegal, only criminals have guns. (That's a mathematical statement, not a political one, BTW.) But, throughout my travels in the United States, it does seem that under US conditions, places where guns of most kinds are legal do seem to be more...polite, shall we say, for values of "polite" that appeal to this dumbe ol' conservative grunt.

I'd just presume chronology preservation, and that all observers would agree on a seuqence of events after they interact with lightspeed evidence of events. And I'd probably stick to a free-form type of FTL that allows limited range jumping, like Asimov's or Dickson's.

Tony: The point I'm trying to make about the closed structure is not that people are afraid of poking holes in the walls, but that the level of surveillance would be almost total. There's just no way to smuggle anything other than a butter knife or a pipe wrench near to your target without setting off an alarm. Imagine if getting through the next door or corridor meant being screened as thoroughly (but hopefully less intrusively) as going through a contemporary airport. Now I'm sure you can think of a dozen workarounds for this scenario, but that would be the point: how did they sneak that weapon in here?

But we're getting away from the main point of why we make all these special circumstances to allow for hand-to-hand combat (whether by knife, lightsaber or zero-gee-jitsu). The reason we want our hero and villian to look each other in the eye as they fight to the death, as opposed to the more realistic option of annihilating one or the other from a few light-seconds distance is that it's more dramatically satisfying. We can all agree on that, I'm sure. I'm just suggesting that having a pacifist, unarmed social order in the background might be a little more realistic than trying to invent a new branch of physics to justify face-to-face confrontations. But there are probably plenty of other options for reaching the same circumstances.

BTW, I'm not knocking Dune. It's one of my favorite books. The personal shield generator just didn't sit as well with me as the other elements. I mean, if you can enforce a galaxy-wide ban on computers, can't you do the same for weapons? We end up with the exact same plot, after all. The point of the ban on computing devices is that it forced human beings to reach for their full potential, rather than letting machines do everything for them. A ban on weapons other than knives and swords would accomplish a similar end, and also limit "wars" to ritualized combat such as dueling, and thus keep the collateral damage to a minimum...

"...and that all observers would agree on a seuqence of events after they interact with lightspeed evidence of events."

It's not just about the lightspeed evidence, man. Lightspeed delays are what keep causality together in the face of varying sequences, not the reason the apparent order differs. Differing sequences are baked into relativity, special or general. It's not just an illusion.

A special frame for all FTL keeps time travel out of things, but doesn't automatically negate the warping of chronology in STL.

Luke:

The one problem with combining freeform FTL and quantum chronology protection would be the weaponization of the effect. If the effect destroys more than just the offender, it wouldn't be long before an enterprising constellation commander sends a drone craft with a strong FTL drive to sabotage the arrival of the enemy's reinforcements, or a terrorist time-mines a crowded shipping route.

"From my POV, this thread's blueshifted all the way into the ultraviolet!"

It also occurs to me that with Blogger's overeager spamfilter, we're seeing responses to posts which haven't appeared yet. We even have our special frame in the form of the email notifications - those of us following from hyperspace get a total ordering of events, not just a partial one.

Thus a spacecraft must come to a complete stop- bear in mind that the planets, solar system, local star group, and the galaxy and galactic group, etc are all moving.

A heck of a lot of porpellant thus needed for a nuclear electric craft, and you can't just teleport into orbit, as the planet will pass you by- you have to accelerate to match the speed of your destination.

"A special frame for all FTL keeps time travel out of things, but doesn't automatically negate the warping of chronology in STL."

I think we're talking about two different things here. When I say that all observers would agree, I don't mean that any observer has special knowledge or a preferred location. I mean that all observers, once they did the math on the light propagation time of their evidence, would agree that an FTL ship that proceeded from Sol, to Wolf 359, to Sirius, in fact did so, in that order.

"I think we're talking about two different things here. When I say that all observers would agree, I don't mean that any observer has special knowledge or a preferred location. I mean that all observers, once they did the math on the light propagation time of their evidence, would agree that an FTL ship that proceeded from Sol, to Wolf 359, to Sirius, in fact did so, in that order."

No, we're talking about the same thing. You'd need a special frame of reference for FTL travel to do that. Otherwise, just working with the GR wormholes we've calculated, observers in those three frames of reference will never, ever agree on the order. Even after correcting for lightspeed delay.

I can't imagine a need for constant, ubiquitous surveilance to begin with, unless the superiors simply could not trust the subordinates. But in that case you would have a mutiny or a civil war going on, and sensors would be preemtively destroyed by whoever was even slightly disadvantaged by the.

Also, I don't believe in inherrently peaceful societies, just ones that are temporarily wealthy and satisfied enough not to make every conflict a matter of using physical force.

WRT Dune, we have to remember that the ban on computers had to do with a perceived loss of humanity to computers. That's a very Sixties attitude that doesn't stand up very well today, but, within its own context, can be accepted. A similar ban on weapons wouldn't work because escalation dominance in use of force is an inherrently human thing. (Because what some are so arrogant to call "inhuman", "cruel", or even "attrocity" are perfectly natural things for people to do, given the right incentives.)

"No, we're talking about the same thing. You'd need a special frame of reference for FTL travel to do that. Otherwise, just working with the GR wormholes we've calculated, observers in those three frames of reference will never, ever agree on the order. Even after correcting for lightspeed delay."

If you'll go back a few steps, you'll find I changed track from wormholes to FTL in general, and how to deal with it in stories, in Re: Rick. I stated that a specific presumption would have to be made: chronology preservation. So all observers would, in fact, agree upon chronology, once corrections for location and lightspeed propagation of information were made.

"If you'll go back a few steps, you'll find I changed track from wormholes to FTL in general, and how to deal with it in stories, in Re: Rick. I stated that a specific presumption would have to be made: chronology preservation. So all observers would, in fact, agree upon chronology, once corrections for location and lightspeed propagation of information were made."

Okay, then you're talking about a special frame for FTL, not quantum chronology protection. A special frame could perhaps be considered a form of chronology protection, but not in the same way Hawking was talking about when he made his conjecture.

"Okay, then you're talking about a special frame for FTL, not quantum chronology protection. A special frame could perhaps be considered a form of chronology protection, but not in the same way Hawking was talking about when he made his conjecture."

I'm not making any assumptions about anything. I'm saying that a fictional FTL system, no matter how it works, should preserve chronology. I don't see an absolute requirement for a special reference frame. I don't see a requirement for an explanation at all. It's just a rule of the milieu -- chronology is preserved, and all observers, after working their sums, will agree that chronology is preserved.

Taking that approach, one doesn't even have to handwave, because the subject need never come up. You hop in your space cruiser, zip off to Wolf 359, then zip off to Sirius, and one happens after the other, because that's the order you proceeded in. Only an author who wants to be a smartass would do otherwise. (And he'd probably wind up just being an ass.)

"Taking that approach, one doesn't even have to handwave, because the subject need never come up. You hop in your space cruiser, zip off to Wolf 359, then zip off to Sirius, and one happens after the other, because that's the order you proceeded in. Only an author who wants to be a smartass would do otherwise. (And he'd probably wind up just being an ass.)"

I think a brief twitch of the hand in that direction wouldn't hurt, if only to placate those who do care. It doesn't take much - while you're mentioning the Whatever Drive and its limitations, just drop a reference to a special frame while talking (however briefly) about how the smartass engineers finally outfought Einstein's shadow.

The one problem with combining freeform FTL and quantum chronology protection would be the weaponization of the effect. If the effect destroys more than just the offender, it wouldn't be long before an enterprising constellation commander sends a drone craft with a strong FTL drive to sabotage the arrival of the enemy's reinforcements, or a terrorist time-mines a crowded shipping route.

Since it is the weakest link in the chain that would break, an attacker would have to make sure his FTL gizmo is bigger and badder than everyone else's. In the case of the terrorist time-mining a crowded shipping lane, the chronology zap would be spread out through all the law abiding travelers, but would be concentrated on the terrorist's gizmo. Unless the terrorist has a very sturdy gizmo, his is the one that breaks.

Tony:

I'm not making any assumptions about anything. I'm saying that a fictional FTL system, no matter how it works, should preserve chronology. I don't see an absolute requirement for a special reference frame. I don't see a requirement for an explanation at all. It's just a rule of the milieu -- chronology is preserved, and all observers, after working their sums, will agree that chronology is preserved.

Taking that approach, one doesn't even have to handwave, because the subject need never come up. You hop in your space cruiser, zip off to Wolf 359, then zip off to Sirius, and one happens after the other, because that's the order you proceeded in. Only an author who wants to be a smartass would do otherwise. (And he'd probably wind up just being an ass.)

Unfortunately, how you describe this is impossible. With chronology protection or special frames, you can set things up so that if someone leaves Sol, goes to Wolf 359, then goes to Sirius, and finally returns to Sol then he will always return after he left. However, some observers will figure, according to the clocks in their reference frames, that he arrived at Sirius before he arrived at Wolf 359, or even before he left Sol. That's relativity for you, and there is no way around it. Fortunately it does preserve causality, so why worry about the time ordering of distant events?

Well, okay, there is one way to have all observers agree on the time ordering of the journey, and that is if the trip is everywhere slower than light. Unfortunately, that is not what everyone seems to want for their space opera.